How did phobia ever come to mean hatred?

Phobia: (Etymonline):

• "irrational fear, horror, aversion," 1786, perhaps on model of similar use in French, abstracted from compounds in -phobia, from Greek -phobia, from phobos "fear, panic fear, terror, outward show of fear; object of fear or terror," originally "flight" (still the only sense in Homer), but it became the common word for "fear" via the notion of "panic, fright"

I think that the meaning of fear and panic are naturally associated with something you dislike or hate, from which probably the association of phobia with hatred.

Homophobia is defined as:

• dislike of or prejudice against homosexual people . (ODO )

• irrational fear of, aversion to, or discrimination against homosexuality (M-W) )

• fear, hatred, or mistrust of lesbians and gay men.(AHD )

From www.quora.com

• The word as coined did refer to a fear, specifically a fear of being near homosexuals or being thought homosexual. The psychologist who coined it, George Weinberg, believed that hatred of homosexuals stemmed primarily from that literal fear. Thus, regardless of the accuracy of Weinberg's thesis, homophobia became shorthand for hatred of homosexuals

• (Weinberg's book, Society and the Healthy Homosexual)

The key element of a phobia as a mental disorder is its irrationality. No one will claim that you're suffering from pyrophobia if you run out of a burning building. Calling a particular prejudice a phobia is an attempt to call out the irrational component of that prejudice.

There is a parallel to "homophobia" in descriptions of prejudice against black people. The Ngram Viewer records a spike in the usage of "negrophobia" during the American Civil War. "Racism" and its variants are more modern terms, but defenders of slavery would probably not objected to these labels as they had elaborate, paternalistic, and rationally-argued reasons for their subjugation of Africans. Their opponents refused to accept this stance by highlighting the underlying irrationality and hatred involved.

Well, the word "homophobia" is a political word invented for political purposes. [Per discussion below, perhaps a more accurate statement would be: "A word primarily used today for political purposes." I'm leaving my original wording so the discussion makes sense.] Trying to break it down into component parts doesn't result in etymological sense. "Homo" = "same", "phobia = "fear", so ... fear of the same? Fear of sameness? But that's not what people use it to mean.

The word was invented by people trying to cast anyone who disagrees with them as having an irrational psychological disorder. Of course a person could believe that homosexuality is morally wrong, or unhealthy, or bad for society, without either having an irrational fear of homosexuals or hating homosexuals. He might fear or hate them, of course, but not necessarily. Just like, if someone said that he believes that smoking cigarettes is morally wrong and bad for your health, he might have an irrational fear of cigarettes. He might hate cigarette smokers. But not necessarily. He might just believe that it is morally wrong and bad for your health.

Are there people who have an irrational fear of homosexuals, in the same psychological sense in which some people have an irrational fear of closed spaces (claustrophobia), or an irrational fear of cats (ailurophobia), etc? Maybe. But most of the people classified as "homophobic" disapprove of homosexuality on moral or religious or social grounds. They don't normally started sweating and shaking with fear because a homosexual entered the room. Classifying everyone who disagrees with you as mentally ill is a handy way to shortcut debate.

(I'm sorry if this answer is "political", but it's a political word and any discussion that does not mention the politics is seriously incomplete. Like if someone asked what the word "entropy" means, I don't know how I could reply without bringing physics into the conversation. Discussing the word as a literal psychological diagnosis is a political statement from the opposite end.)

It should be noted that the suffix "phobia" or "phobic" doesn't always actually refer to a psychological phobia in the strict sense of an irrational fear. For instance, some substances are said to be "hydrophobic" because they separate from water when mixed.

Having said that, in this case, as Josh's answer points out, the word "homophobia" did originate with a psychologist who apparently thought disliking homosexuality was a result of an irrational fear of it. Perhaps in some cases this is actually true, but the term nowadays seems to be commonly used to deride anyone who thinks homosexual acts are wrong or is opposed to some or all of the 'homosexual rights' political agenda, regardless of whether they have any actual fear or hatred of homosexuality or those who practice it.

Merriam-Webster on 'phobia,' '-phobia,' and 'homophobia'

Merriam-Webster's Eleventh Collegiate Dictionary (2003) gives one definition for the noun phobia but two definitions for the suffix -phobia:

phobia n (1786) an exaggerated usu. inexplicable and illogical fear of a particular object, class of objects, or situation

-phobia n comb form [no first date identified] 1 : exaggerated fear of {acrophobia} 2 : intolerance or aversion for {photophobia}

The freestanding noun phobia first appears in a Webster's Collegiate Dictionary in the fifth edition (1936) of that series:

phobia n. Psychol. An irrational, persistent fear of a particular of a particular object or class of objects.

That same dictionary has this entry for the suffix -phobia:

-phobia A combining form denoting fear, dread, and often implying dislike or aversion;—used esp. in Med. & Psych. with names of things toward which phobias are directed, as in Anglophobia.

The first Collegiate Dictionary to include an entry for the suffix -phobia is the Third Collegiate (1916)—and the "dislike" sense of the suffix is already in place:

-phobia A suffix denoting fear, and often implying dislike or aversion.

Although it is not as old as the "exaggerated fear" sense of the suffix, the "intolerance or aversion" sense of the suffix has been in use for more than 200 years, albeit in a context that involves an aversion grounded in physical discomfort. Photophobia—which the Eleventh Collegiate defines as "intolerance to light; esp : painful sensitiveness to strong light"—dates back to 1799. The oldest -phobia that I've identified is hydrophobia, from 1547, which originally meant "rabies." (The connection between a viral disease and a "fear of water" is, according to Wikipedia, that "in the later stages of an infection ... the person has difficulty swallowing, shows panic when presented with liquids to drink, and cannot quench his or her thirst.")

But many -phobia terms that are widely used today in nonspecialist speech—acrophobia (1892), agoraphobia (1873), arachnophobia (1925), claustrophobia (1879), and commitmentphobia (earliest Google Books match: 1981), among others—are considerably younger than photophobia.

Of particular interest to the poster (and many of the answerers) of this question is the term homophobia, which the Eleventh Collegiate says goes back to 1969:

homophobia n (1969) irrational fear of, aversion to, or discrimination against homosexuality or homosexuals

The term debuted in the Tenth Collegiate (1993), with the identical wording. The definition is interesting in that it embraces both "fear of" and "aversion to" senses of -phobia and adds a third option, "discrimination against."

A side-trip to 'Anglophobia'

The choice of Anglophobia in the Fifth Collegiate as an example of -phobia in action is interesting: Does it refer to an irrational fear and dread of England and the English, or to an intense aversion or even just to a dislike of them? A psychiatrist might have one response to that question; an outspoken proponent of Argentinian sovereignty over the Falkland Islands, another. The Eleventh Collegiate takes the latter view of the allied term Anglophobe:

Anglophobe n (1866) : a person who who is averse to or dislikes England and things English.

But the corresponding definition in Webster's International Dictionary (1890) stops at this:

Anglophobia n. intense dread of, or aversion to, England or the English.

The "Intense fear or aversion" language gives way to merely "intense aversion" decades later, in the Seventh Collegiate (1963), which simultaneously sets a lower standard for Anglophobe: "a person who is averse to England and things English." The definition of Anglophobia disappears in the Eighth Collegiate (1973), which treats the word as an extension of Anglophobe. The wording "or dislikes" first appears in the definition of Anglophobe in the Ninth Collegiate (1983) and (as suggested above) has been in place ever since.

When did '-phobia' in popular usage come to include the sense 'hatred' or 'dislike'?

We've already seen a definition of -phobia from 1916 that explicitly describes the suffix as "often implying dislike or aversion."

That the "fear"/"aversion" split was well established in everyday speech by the beginning of the 1980s is evident from the split list of synonyms for phobia that appears in Jerome Rodale, The Synonym Finder (1978):

phobia, n. 1. fear, irrational fear, abnormal fear, obsessive fear; dread, horror, panic, terror, angst, fear and trembling, anguish, anxiety, apprehensiveness, apprehension, misgiving, suspicion, distrust, qualm, worry, disquiet, disquietude.

2. aversion, hatred, dislike, distaste, peeve, pet peeve; disgust, odium, detestation, abhorrence, antipathy, repugnance; abomination, loathing, execration, detestation; disrelish, displeasure, repulsion, revulsion, nausea; craze, obsession, neurosis, mania, monomania, paranoia.

Early meanings of 'homophobia' in the context of psychotherapy

Today, it seems to me, homophobia is often used in common parlance to mean "strong dislike of homosexuality or homosexuals for whatever reason." But in the literature of psychotherapy, writers in the 1970s and early 1980s made an effort to define homophobia as a form of dread.

In his 1983 introduction to a reissue of his 1972 book, Society and the Healthy Homosexual (1983), George Weinberg claims to have been the originator of the term homophobia:

Out of my study [during the 1960s of the then-prevailing societal attitude toward homosexuality] came the recognition that I was up against a phobia—an irrational revulsion so widespread that it had gone unrecognized by most people. Anthropologists have pointed out that societies overlook their own broadest biases; such biases affect the very lens through which we see. We do not think we think a thing; we imagine it is so. And thus the irrational condemnation of homosexuals, which has resulted in so much violence deprivation, and separation from potentially good friends, went largely unobserved.

In 1967 I invented the name "homophobia" to describe this irrational reaction, and I analyzed this response to homosexuality in a series of articles. Though I have written for many national magazines, only the underground press would publish these. When this book was finished [in 1972], eleven publishers turned it down, some perhaps because they thought it of inferior quality but almost certainly others because they dreaded association with such a point of view.

In the opening chapter of his book, Weinberg defines homophobia as

the dread of being in close quarters with homosexuals—and in the case of homosexuals themselves, self-loathing

Two articles included in John Gonsiorek, Homosexuality & Psychotherapy: A Practitioner's Handbook (1982) try to define the particular features of homophobia within a broader range of disapproval. Martin Rochlin, "Sexual Orientation of the Therapist and Therapeutic Effectiveness with Gay Clients" echoes Weinberg's definition and then contrasts it with what he calls "a more insidious form of anti-gay prejudice":

Homophobia may be defined as the irrational dread and loathing of homosexuality and Homosexual people (Weinberg, 1972). Heterosexism, a more insidious form of anti-gay prejudice, refers to the culturally conditioned bias that heterosexuality is intrinsically superior to homosexuality.

In David McWhirter & Andrew Mattison, "Psychotherapy for Gay Male Couples," homophobia constitutes one type of "anti-homosexual attitude":

Anti-Homosexual Attitudes

... These [anti-homosexual] attitudes include: 1) ignorance, 2) prejudice, 3) oppression, and 4) homophobia. All together, or in some combination, are overtly or covertly present in every gay male couple we have ever seen. ... A careful assessment and differentiation among the four attitudes is important as the couple's therapy begins.

Of these four anti-homosexual attitudes, homophobia is the most insidious and difficult to identify and treat. A diagnosis of homophobia is confirmed by ruling out the other anti-homosexual attitudes. Ignorance is changed by knowledge. ... It requires more than knowledge to change prejudice: There must be some impactful positive emotional experience, such as can occur within a group. Oppression, especially self-oppression, may take the form of unwitting assumptions about the negative attitudes of others toward homosexual persons. Homophobia is recognized by its persistence in the face of knowledge and the reduction of prejudice. The continued presence of low self-esteem and lack of self-acceptance, resistance to coming out, and the continued rejection of some aspects of homosexuality are evidence of homophobia's virulence.

Evidently, in the relatively early days of the term's existence, homophobia was used—in the first instance by gay psychotherapists—to indicate a deep and irrational psychological condition of fear of homosexuality, and it was applied as much (though perhaps in a somewhat different sense) to both gay and nongay people. Most significantly, I think, it was essentially a clinical term.

Of '-phobia,' '-phobes,' and politics

From a political perspective, being described as suffering from an irrational fear is problematic. To the extent that a -phobe of any kind is viewed as a fearer rather than as a disliker, the person has by definition been preemptively disqualified from the capacity to have a rational, nonemotional basis for opposing the object of his or her fear. Clearly, the "irrational fear" implication of words like Anglophobe and homophobe—even if that isn't the only possible way to interpret the meaning of the term—does not set the stage for a reasoned debate on the merits of disliking the English or of disliking homosexuality—it simply dismisses the "aye" position as irrational.

What makes calling someone a -phobe so powerfully dismissive is that it implies a scientific basis for the criticism—and despite the skepticism one can find with regard to certain points of scientific inquiry in the West, science commands huge respect here. Indeed, the scientific assessment of homosexuality (for most of the twentieth century) as a mental disorder or psychiatric illness did much to prevent both the courts and the general public from taking seriously as a political issue the severely disadvantaged legal status of homosexuals in society.

The Wikipedia page for gynophobia notes that influential experts such as Havelock Ellis viewed male homosexuality as being, in part, a product of an abnormal fear of women:

Gynophobia was previously considered a driving force toward homosexuality. In his 1896 Studies in the Psychology of Sex, Havelock Ellis wrote:

It is, perhaps, not difficult to account for the horror—much stronger than that normally felt toward a person of the same sex—with which the invert often regards the sexual organs of persons of the opposite sex. It cannot be said that the sexual organs of either sex under the influence of sexual excitement are esthetically pleasing; they only become emotionally desirable through the parallel excitement of the beholder. When the absence of parallel excitement is accompanied in the beholder by the sense of unfamiliarity as in childhood, or by a neurotic hypersensitiveness, the conditions are present for the production of intense horror feminae or horror masculis, as the case may be. It is possible that, as Otto Rank argues in his interesting study, "Die Nacktheit in Sage und Dichtung," this horror of the sexual organs of the opposite sex, to some extent felt even by normal people, is embodied in the Melusine type of legend [Melusine was said to be transformed every Saturday into a half-woman/half-serpent form].

From one point of view, it may seem ironic that George Weinberg and other early gay psychotherapists would be inclined to analyze aversion to homosexuality as an irrational and involuntary mental state—in short, as a mental disorder. But from another point of view, nothing could seem more natural than for people whose sexual preference and identity, for decades, led them to be criminalized, denied certain fundamental civil rights, and disparaged as abnormal on the basis of scientific analyses to counter with scientific analyses of their own.

In any event, the term homophobia as used loosely in nonspecialist discourse seems to have moved away from the psychological notion of "irrational fear of homosexuality" and toward a simpler sense of "dislike of or aversion to homosexuality," though the psychological underpinnings are undoubtedly still there at some level.

Conclusions

Merriam-Webster's current definitions of -phobia endorse its use in instances of "irrational fear" or "aversion," without spelling out whether the aversion (like the fear) must be "irrational." Early authors using the term homophobia in the context of psychotherapy focused on its characteristics as an irrational fear, but more-recent popular usage has blurred or obliterated any clinical sense of the word with a generalized notion of hostility toward or disapproval of homosexuality. The use of -phobia not merely to indicate fear but to imply dislike or aversion goes back at least a century, since it appears with that definition in Webster's Collegiate Dictionary, third edition (1916).