Marriage Equality

I was struck by this graphic that I came across today. Wow how things are a-changing! The geek in me can't help but notice how linear/straight the lines are. One thing I've never understood about the gay marriage debate is why doesn't the "full faith and credit" clause of the consistution require each state to recognize gay marriages performed in another state. I can understand how a state could legislate that it wouldn't issue marriage licenses for same-sex couples, but instituting a law the specifically and directly states that one state will not honor a marriage performed in another seems clearly unconsitutional. Then again... I'm not a lawyer so what do I know.