This is exactly why no one in their right mind could support "states' rights"
And if the national government was doing something like this, would you then suddenly switch to be in favor of states rights?
Can you cite an example of the federal government attempting to ban an AP course?
I can readily cite examples such as drug prohibition and capital punishment where federal policies are decidedly more conservative than some states. For that matter, assume that not only DOMA had been upheld, but that the Supreme Court had ruled that the States couldn't decide on their own to recognize SSM. There are few people who decide whether they are for or against states rights without considering which would be more advantageous for their own policy preferences on specific topics. Since you were apparently basing your position on how it affected another issue, I doubt that your opposition to states rights was based upon a sincerely held belief that centralized decision making is superior regardless of the results.