Wow... some interesting comments here. Admittedly, I didn't make it through the whole thread, but just thought I would add a simple opinion.
The seperation of church and state is ultimately the best guidepost here. The government does not have the right to restrict marriage. Conversely, the government also cannot force the church to accept it. If a gay couple wants to get married, and they can find a church, seperate minister, or DMV that is willing to do it... the government should not stand in their way. With that said, if a particular church refused to marry a gay couple, the government could not step in and force the church to do it.
In either situation, the government must remain neutral.