No emotion, just think this is pretty clear cut. It's nothing like a concealed carriage permit, which is explicitly for only one state with limited reciprocity.
I ran into this - my marriage is by Contract, allowed by my home state's law. No marriage certificate, just the original notarized and signed contract in a safe. Moved to Hawaii years back and my wife, while getting her driver's license ran into some issues - they were originally considering our marriage as a common law marriage, which surprisingly Hawaii doesn't go for (the conservative/liberal divide in Hawaii is really interesting). However upon some research on their part they found that it was indeed legal in the original state of issuance and honored it as such.
I can see where states can say they won't issue same sex licenses (or contracts if they do that), but can't see how they won't honor licenses issued in other states. Don't see the precedent.