The Republican Party has framed itself as a party that supports individual decision-making. Well, gay marriage falls under that.
The Republican Party frames itself as traditional. Well, it seems like homosexuality has been around forever and has been practiced in every society, so how much more traditional can you get?
I know that a lot of people frame this in a religious context. Now, injecting religion into politics is very dicey for me. However, there is nothing in the New Testament that bans homosexual relationships.
The Libertarian wing of the Republican party supports individual freedoms, but many of these same people feel that gay marriage will damage 'traditional marriage.' Divorce rates are over 50%. Can gay folks do worse than straight folks on this? If gay people are able to build stable families with kids and be homeowners, isn't that good for America?