It doesn't, unless you're a homophobe.
I disagree. Homosexuality is a deviation from normalized behavior, so to say that the mere idea that people might recoil from homosexual acts or behavior is homophobia in itself is a bit strong. Thats not to be confused with actual homophobia, which prides itself on hatred and demonization of not only the acts or behavior, but the people themselves and their rights as human beings.
Its complicated. Ive always been sympathetic to gay rights once I progressed beyond grade school immaturity, but I'd be lying if I said that I was even remotely comfortable with being around homosexuals, or condoning their behavior around my person until very recently. Before then I was pretty intolerant, but after exposure to gay people you realize universal truths about respecting humanity that you knew all along, but couldnt articulate until you actually gained personal experience with the group that inspires discomfort.
As a society we're progressing. Myself included.