Why is the comma splice an error?

Is it more accurate to call punctuation rules 'traditions' or 'conventions'?

To my mind, the word "convention" refers to a shared practice that was adopted to serve some perceived practical purpose and that continues (at least arguably) to serve such a purpose today, whereas a "tradition" refers to a shared practice that need not have any other justification for its continuing existence that that we or our predecessors did it in the past.

I would use the term "convention" rather than "tradition" to describe usage rules such as the one against using a comma to separate independent clauses that are not connected by conjunctions. Likewise, putting a period rather than a comma at the end of a declarative sentence is a convention, and so is using single or double quotation marks rather than commas to indicate a "words used as word." It is certainly possible to replace all of the conventional punctuation marks in the paragraph I am now writing with commas—treating them as, in effect, a unitary way to convey the idea, "a punctuation mark of some kind goes here"—and still have a consistent graphical representation of a grammatical utterance. Looking at it, however, you can see why writers and readers might find conventions that entail the use of punctuation marks besides commas (in addition to the convention of using capitalization to indicate the beginning of a new sentence) for particular purposes to be quite valuable:

I would use the term, convention, rather than, tradition, to describe usage rules such as the one against using a comma to separate independent clauses that are not connected by conjunctions, likewise, putting a period rather than a comma at the end of a declarative sentence is a convention, and so is using single or double quotation marks rather than commas to indicate a, word used as word, it is certainly possible to replace all of the conventional punctuation marks in the paragraph I am now writing with commas, treating them as, in effect, a unitary way to convey the idea, a punctuation mark of some kind goes here, and still have a consistent graphical representation of a grammatical utterance, looking at it, however, you can see why writers and readers might find conventions that entail the use of punctuation marks besides commas, in addition to the convention of using capitalization to indicate the beginning of a new sentence, for particular purposes to be quite valuable,

The language is the same. All I've done is replace more-or-less standard conventions for using quotation marks, periods, dashes, parentheses, and sentence-case initial capping with comma-only punctuation and capping only of the pronoun I. Has the grammar changed? No—not if you accept the view that grammar is fundamentally an attribute of spoken language. Punctuation isn't spoken; it's added to the plain words of speech in writing to clarify the internal connections of certain words, phrases, and clauses. Consistent, conventional punctuation helps readers follow the flow of writing with a minimum of misreadings, false starts, and sheer bewilderment.

Because it is based on convention rather than on linguistic necessity, punctuation is sometimes treated as an arbitrary and artificial construct of ignorant or officious rule enforcers—"fake grammar," as it were. But in orthography, as in other spheres of human activity, convention is a powerful force for coherence and shared meaning.

What justification is there for the rule against comma splices?

Viewed in isolation, the convention against comma splices may seem unnecessary and ultimately unjustified. After all,

I never liked school, it was boring and repetitive most of the time.

isn't materially more difficult to parse than

I never liked school. It was boring and repetitive most of the time.

or

I never liked school; it was boring and repetitive most of the time.

But when the wording appears in a larger context, issues of interrupted narrative flow and misdirection become apparent. For example:

I know that some people have fond memories of spending most of their waking life in childhood attending school, they recall the joy of learning, the camaraderie with fellow students, and the opportunity to explore creative tasks, I never liked school, it was boring and repetitive most of the time.

The only unconventional aspect of this block of text is its rejection of the convention against comma splices. Three sentences become one; and because the text is punctuated as a single continuous sentence with two internal comma splices, the word they—which would start a new sentence if the text were punctuated conventionally—is not initial-capped. The comma splices damage the flow of the text and force readers to feel their way carefully through the text to make sure that they haven't run through an ambiguous stop sign and misread the sense of the clause that follows each comma.

The conventional rule against comma splices thus promotes a valuable purpose in limiting the province of things that a comma (which in any event may perform a multitude of functions in writing) can properly signal. By insisting that colons, semicolons, and periods—but not commas—should play the role of indicating abrupt breaks in written text at the end of complete clauses, the convention frees readers from having to include "hard break signal" among the possible meanings of any particular comma they encounter.