Word that is to "sexual orientation" as "racism" is to "race"?

Solution 1:

Heteronormativity will suit.

Per Oxford Dictionaries Online (ODO):

Heteronormativity: Denoting or relating to a world view that promotes heterosexuality as the normal or preferred sexual orientation:

the heteronormative codes of twentieth-century mainstream Western cinema

Per Wikipedia:

Heteronormativity is the belief that people fall into distinct and complementary genders (man and woman) with natural roles in life. It assumes that heterosexuality is the only sexual orientation or only norm, and states that sexual and marital relations are most (or only) fitting between people of opposite sexes. Consequently, a "heteronormative" view is one that involves alignment of biological sex, sexuality, gender identity and gender roles. Heteronormativity is often linked to heterosexism and homophobia.

A more specific (and more recently-introduced) related term is cisnormativity.

Per Wiktionary, for example:

Cisnormativity ‎(plural not attested):

The assumption that all human beings are cisgender, i.e. have a gender identity which matches the sex they were assigned at birth.