So, you're against the state's rights when it's one of your issues.
This issue is different, because the pressure will come on all states to conform once a few states begin.
Some things do need to be federalized. I'm in favor of adhering to the constitution. I'm against using federal matching funds to intefere in things that should be explicitly state rights. But there are things that need to be federalized that are not presently in the scope outlined for the federal government. And that does call for Constitutional amendments.
So, you're against the state's rights when it's one of your issues.
There is a difference between regulating something and defining something. States may have the right to regulate the drinking age, but that doesn't mean that they have the right to define the chemical composition of alcohol or define the meaning of "100 proof". By the same token, states have the right to 'regulate' marriage in terms of the restrictions that they put on it, but that doesn't mean that the states have the right to DEFINE marriage. They are two entirely different things. One belongs at the state level, and the other, apparently, needs to be done at the federal level.