The problem is, the opposition of same sex marriage is divorced from practical reality. In the District of Columbia SSM is legal and sociey is the same there as it was before aside from a few more married couples. None of the practical criticisms that have been voiced by social conservatives such as increased suicide rates, crime, etc have came to pass. Some of the claims that were made were just ludicrous.
So lacking any tangible factor, all that can said is that they don't like it, but that is no reason at all for government to take a position. We don't like Nazis but we allow them thier freedom of speech, yet we don't want to allow homosexuals the pursuit of happiness?
And as far as the founding fathers go, I could care less what they thought, they were just bourgeois politicians, I see no reason to ascribe any sort of value to them above bourgeois politicians of this day and age.