Why is there even a gay marriage debate? This is the land of the free, not the land of extreme fundamentalist Christians. If you don't like the idea of a gay marriage, then don't get into a gay marriage.
But, to ban it is discrimination, no matter how you look at it. Luckily, we have something called separation of church and state that prevents people from bludgeoning others with their own religious beliefs, such as the idea of marriage between man and woman simply because the Christian Bible says God made Adam and Eve.
Not everybody adheres to this idea, so there's no reason to deny people the right to marry who they want to.