Honestly I am not convinced that being repulsed by gay sex is indicative of active hate. However, I don't buy the notion that it is a natural feeling. I think that in large part, what we find attractive/repulsive is influenced by culture. The easiest way to see that is with food. Surely something such as what we find tasty must be purely biological right? Well it clearly isn't. Americans aren't born with a genetic predisposition to find things like duck necks, bull testicles, cow heart, etc... disgusting. We aren't genetically predisposed to find those eggs with the dead chicken in them disgusting. We find those foods disgusting because we simply aren't exposed to them often in our culture.
I think that finding two gay men kissing "gross" is likely only repulsive to many because our culture is in many ways still homophobic. Straight men can be accepting of gays, but can't actually show acceptance of gay acts because then they might be seen as gay. So the simple way to show you aren't gay and don't want to participate in gay acts is going "ewww gross." That doesn't make the person saying that actively homophobic, but the act is definitely rooted in more subtle homophobia.
The good news is that it actually can be changed. I'm going to guess that people exposed to gay public displays of affection eventually become desensitized to it and no longer find it gross. Nudist communities aren't made up entirely of smoking hot nude people. There are people we would find "gross" naked, but other nudists don't see it as gross because they are so frequently exposed to it.
.
