I probably already said something similar to this a while back somewhere, but meh: Marriage in America currently exists as a joint operation between the church and the state. As things stand now, we can't legalize gay marriage, because if the state changed the definition of marriage from what it's been here pretty much since the founding of America, it would essentially be dictating to the church what they have to believe. If you want gay marriage, or something similar, you'd first have to split the concept of marriage up -- making the word "marriage" refer to a solely personal religious institution, which each church or group of churches (or mosques or synagogues or whatever) can define on their own, and put all the legal benefits of what we currently call marriage into a contract, overseen by the government, that any two people can make with each other.