I've thought long and hard on this subject. It's one fraught with a lot of emotion and it is loaded with religious overtones.
I'm a Christian. I'm a member of a somewhat liberal Lutheran Church, but many of us in the congregation are veterans and conservative ones to boot.
I'm also straight and married. Mrs. VW happens to be the sweetest woman God ever put on this earth and why I got so fortunate to be the one married to her is beyond my ken.
All that said, here are my thoughts on the matter.
Marriage was long ago hijacked by the state. The ceremony might take place in some form of house of worship and the person officiating might be a cleric of some kind, but all he or she does is stand in for a judge. You had to buy the license (obtain state permission) and your preacher/priest/rabbi/coven leader had to register in some way with the the state or local government in order to perform the marriage. (There may be a few places that require them to pay a small fee as well, I don't know).
In the eyes of the state, your marriage is actually a civil union. To the Bureaucrats, a mayor or a judge is no different than an ordained minister.
So in essence, if a homosexual couple wants to marry, I don't particularly care. As long as it is a state licensed activity, it needs to be available to all.
Here is how I think it should be done. If you want to marry someone, you go buy your license according to established laws. After the waiting period (if applicable), you return to the clerk who signs it and then the clerk gives you a copy. You are now civilly united. If you want your marriage to have a ceremony of some sort or want it sanctified by whatever faith and they agree, then have at it. That part would be voluntary and up to you.
Regardless of the second part being voluntary, someone will try and force, by judicial fiat, a church that does not recognize gay marriage to officiate in the religious part of the ceremony. That would be wrong. Many churches and denominations say that homosexual acts are a sin. That is their right under the first amendment and so it should remain. There are some churches that don't see it that way and that is also their right. If a minister wants to perform a religious ceremony for homosexuals and their denomination agrees, then by all means perform the ceremony.
The first amendment means what it means, even if someone doesn't like it.