As a married christian libertarian, I find it difficult to fathom how everyone gets so worked up about this. To me it seems rather simple, I am twice married in the eyes of two different institutions: God and the government. Almost 9 years ago I stood before God and all the earthly people I hold dear and I pledged my life to the woman who is now my wife, and she reciprocated, and we were then married.
After all that was said and done, we got together and we let the government know through legal documentation that we were now married and the government decided to grant us a specific tax status and various other considerations for whatever reasons it is that the government does the things which it does.
If people want the government to grant the same recognition to gays who pledge their life to each other, then I say more power to them. It doesn't affect me, and it doesn't affect my marriage, which is before God, not the IRS.
I might just as well get upset about straight couples who get married outside of a church. If a straight couple goes to a justice of the peace and pledge their life to each other, and receives some government benefit from it, am I as a christian supposed to be upset about that? I don't think so.
I used to be slightly offended by the mis-use of the term "marriage" in "gay marriage", but I don't even care about that anymore. Have you ever seen a car advertisement talk about "the marriage of beauty and power" or some such nonsense?