While I don't think the proposed reasons are inherently wrong, I do want to put forward another potential explanation that's been bouncing around my head.
I suspect the practice of gender/sex segregation has a lot to do with the fear. One idea behind segregating the biological sexes is that the men (who are, of course #sarcasm, slobbering animals who can't control their sexual urges) won't put the women in danger, and the women (who are, obviously #sarcasm, inherently weak and effeminate and highly emotional) won't take away the mens' manly masculinity. In this model, if any of the men in the mens' club are homosexuals, then they're seen as a danger because of mens' inherent rampant and uncontrollable sexual desires; they'll rape the other men and make them all effeminate in one fell swoop.
With this demonization comes the inherent abuse of bisexual men, who are fed fears of "turning gay" and could become severely depressed and self-loathing as a result. (As a side note, I strongly suspect that the nonsensical idea of "homosexuality as a lifestyle choice/nothing but lust" was started, and largely perpetuated, by people who are self-denying bisexuals, who don't realize that heterosexuals feel no sexual attraction for their same biological sex, and that homosexuals likewise feel none for the other.)
And none of this is even TOUCHING on the strongly related TQ part of the LGBTQ+ movement, which also throws a strong wrench in this whole mess. People who are asexual, demisexual, transgender, intersex, genderfluid, or any other form often get ignored in these discussions, and I suspect this is because the existence of such orientations/gender-identities basically disprove all of the "reasons" for hating, shunning, or fearing homosexuality.