>>4357579 (OP)Reproductive duty.
STD-proliferation.
Gay-mafia-nepotism with skewed priorities.
Competes with heterosexuality and marriage which is le bad because we need baby making families or something.
Male lust is supposed to be moderated by female sensibilities, unrestricted male lust leads to gross thing like no loads refused mass piss and poop orgies.
Homophobia being a natural disgust response probably evolved for good reasons even if the exact reasons are unknown.
Following your instincts is more pleasurable than suppressing them, therefore all things being equal following your natural inclinations to be homophobic is rational and utilitarian.