I don't approve of fag marriage, but regulating marriage isn't an enumerated power of the federal government. It's a state problem.
Minimal regulation is required - 1. Ensure the marriage is between man and woman. 2. That they are not closely related 3. They are of age. 4. They are acting of their own free will and not already married 5. That they are free of communicable disease. 5. That it is properly witnessed.
This has been done for the last forever number of years with no issue but somehow now it is an issue the government should not get involved with. It doesn't make any logical sense. If anything falls under the general welfare clause - and I know conservatives hate that clause - it has to be the overseeing of marriage which ensures the best possible crop of well-adjusted citizens.
And also, the state is not free to change natural law which would be injustice. The State is required to work within the natural law which our founders recognized and is non-negotiable.