Homosexuality is a gateway sin to bestiality, pedophilia and necrophilia.
Rick Santorum said it best
In every society, the definition of marriage has not ever to my knowledge included homosexuality. That's not to pick on homosexuality. It's not, you know, man on child, man on dog, or whatever the case may be. It is one thing. And when you destroy that you have a dramatic impact on the quality
You let two men get married, just because they love each other, then you mine as well let men marry dogs. After that it is an easy slippery slope to murdering small children and violating their corpses.