People don’t seem to recognize that marriage laws don’t discriminate based on sexual orientation. They discriminate based on gender: a gay man can marry a gay woman. If it does not mention sexual orientation, the constitution DOES consider gender a criterion for equal protection.
I don't see your point. Men are allowed to marry the opposite sex. Women are allowed to marry the opposite sex. The most natural reading of the laws on marriage and their state Constitution is that equal protection requirements are met, even without considering that the primary definition (and until the recent activism the only definition) of marriage is the joining of a man and a woman. The proper route for changing laws that are constitutional is legislation, not litigation, and the gay-marriage advocates are undermining the rule of law by using the Courts to write new laws through dubious rulings.
If I wanted to marry my first cousin (and cute as she is, I don't), I wouldn't be able to do it legally in half the states. Is that an equal protection question too, or is it more properly in the realm where the legislature should be writing the laws? How are the gay marriage and incestuous marriage questions different constitutionally?