The fact that people can be so naive and close-minded when it comes to this issue makes me ashamed to be American. Honestly people, this country was founded on religious freedoms, and in America one of the best things is that everyone's free to believe whichever religion they want, or none at all. So why, in a country that allows us to have the freedom to not adhere to a national religion, are principles contained within that religion being forced upon those who may not even follow those beliefs?
You fundamentalists can quote scripture all you want, but for those who don't believe in your scripture, incessant quotation of it serves no purpose whatsoever.
Maybe marriage is a religious union between a man and a woman, but you know what? It's not a Christian idea, and it is shared by pretty much all other major religions in the world. That said, what possible right could the state have to forbid a religious institution to allow marriage between same-sex couples?
The constitution protects the rights of all American citizens, and same-sex couples are absolutely still American citizens. By guaranteeing everyone's right to religious freedom, they established a specific separation of church state, and forbidding an institution from allowing gay marriage is a direct infringement on that separation.
If a Church doesn't want to allow the marriage of same-sex couples, then that is FINE. It is their right to not allow it in their church, but if there is a religious institution that is willing to perform that union, then in my opinion, no facet of government should have the right to step in and forbid that.