A hydrophobic substance repells water, so "phobic" has always had repulsion as an alternate definition

That's a fair point, but it doesn't account for complete breadth of ways that the term is regularly used in the LGB community. Earlier in this thread, I used the example of Ben Shapiro having a non-emotional, moral objection to homosexual activity. I included the details of him not acting squeamish around Dave Rubin specifically to tease out the definition that you're proposing. Nevertheless, u/reluctant_commenter, whom I respect and who hardly strikes me as a radical or an outlier, clarified that she considers him to be homophobic. Consequently, the word is clearly being used to refer to a much broader set of attitudes than fear or repulsion.

Also, including repulsion in the definition of "homophobic" risks implying that that many gays and lesbians are heterophobic for attitudes that aren't actually bad. I don't consider a lesbian who feels repulsed by the notion of interacting with male genitals to be heterophobic (or misandric). By the same principle, I don't consider straight people who feel some repulsion toward various homosexual acts to be homophobic.

That was a level-headed and thoughtful reply, though. I really appreciate it.