Yes, America, like all countries have gone through a lot of changes regarding how we view race, gender, disability and other uncontrollable factors. Now we are undergoing changes based on controllable factors.
No, its not the same argument as a mixed race marriage. Its pretty simple, One has to inappropriately add additional prohibitive defining terms to make a mixed race marriage illegal. For example marriage is between a (white) man and a (white) woman. WE generally do not allow laws that cite uncontrollable factors as a limiting factor unless safety is involved. An actual change in the definition needs to be made to allow marriage to be something other than a man and a woman. I am fine with States making this change if they desire but it should not be forced by a court.