The biggest factor in homophobia is that it is repulsive. What I mean is that a great many men are repulsed at the thought of fooling around with another man, to the point that they want to pass laws about it.
I think that personally, I wouldn't want to have sex with another man. I also wouldn't want to eat bugs, lick gerbils, dig ditches for a living, live in a cave, or have sex with my mother-in-law. SHOCKINGLY, none of these other repulsive issues are up for a vote.
Something that is quite ridiculous with the whole ban on gay marriage thing is that the part of homosexuality that is most repulsive to people is not being banned, and the factor that is most damaging to marriage is not being banned either! Gays can still have sex, and people can still get divorced. Unbelieveable. This ban approved in my crappy state (Ohio) is POINTLESS.
Furthermore, letting gays marry will NOT lead to massive abnormal legal pairings or groupings such as polygamy or bestiality, any more than alcohol being legal has led to massive legalization of hard drugs like crack or heroin. While I don't see anything wrong with polygamy if consent and majority is present, those two factors are precisely why other forms of marriage will NEVER be legal. Dead people can't give consent. Minors can't give consent. Animals can't give consent. Inanimate objects can't give consent. It's ridiculous to argue otherwise.
However, it ISN'T ridiculous to argue that certain US citizens who work, pay taxes, engage in commerce, own businesses, serve their country, work in their communities, help others, give of themselves, etc., just like everyone else, should be allowed the same freedoms that everyone else has. How do you work the whole "fighting for your freedom" angle on the war in Iraq, for example, when gays don't have the same freedom?