I find this argument pretty interesting. I'm ashamed to admit that I never thought about this before:
I don’t understand the resistance to the idea that the homosexuality taboo is about sexism. Homosexuality and deviation from gender norms (which, of course, are relentlessly hierarchical) are so tightly connected with each other in popular culture that each is normally and easily taken as a marker for the other. A "faggot" or a "dyke" is a person who fails to conform to normal gender norms; the term is routinely applied to people without regard to their sexual behavior.
I don't find the argument completely convincing (and I don't find the hypothetical about "miscegenosexual couples" as preposterous as I'm apparently meant to), but it's clearly an important aspect of this form of discrimination that deserves to be more widely recognized and addressed.