Great question.

I have read a lot of "Oh, the USSC appts are a ruse, the Democrats would block any Pro-life judges" as the rational for the Puma McCain voters.

But, there is SO MUCH more then just Roe repeal heading for the court in the next decade.

No doubt WHO McCain wants to appoint, Federalist Society approved clones in the Scalia mold (or mould if  you prefer.)

How awesome would it be if the state of Alabama had to recognize a gay marriage from California?

It would quickly create strong blue majorities in the South, as many heads suddenly explode.

to the FFC clause.  So if one state did not allow marriages between second cousins, for example, and another state did, the first state could refuse to recognize the FFC clause under the public policy exception.

Similarly, I'd imagine a same-sex marriage would fall into the public policy exception.

I am pretty sure that DOMA doesn't violate the Full Faith and Credit Clause, but I haven't undertaken any kind of technical analysis. However, typically states aren't required to honor licensing decisions (as opposed to court orders) from other states.

A state's decision to recognize marriage is based on its policy decision to provide advantages to those in certain kinds of relationships. (I'm now ignoring whethert the equal protection clause places limitations on how this advantage is distributed; I'll touch on that below.) I don't see why any state is bound to go along with the other states policy decision to issue a license or conditional benefit. If state A decides to provide some type of welfare to person p, then state B doesn't have to provide the same welfare to person p if he or she moves to state B. That's not what full faith and credit is meant to accomplish. It doesn't force one state to adopt the policy of another.

Moreover, longstanding precedent holds that a state need not recognize a marriage entered into in another state with different marriage laws if those laws are contrary to strongly held local public policy. By way of example, this "public policy doctrine" has been applied to foreign marriages between first cousins, persons of different races, and minors. The granting of a marriage license has always been treated differently than a court judgment, which reflects the application of another state's policy and is entitled to full interstate recognition. Entitlement to licenses and similar policy-driven benefits do not follow someone from one state to another and, accordingly, do not require interstate recognition.

All that said, I do think that state laws banning gay marriage are unconstitutional on the grounds that they violate the equal protection clause of the 14th Amendment. However, if a court proceeds from the opposite position, then I don't think it would force one state to recognize the policy decision of another.

Again, though, there are surely some complications and DOMA-specific details that I'm not considering here, which might very well change my opinion. But, looking at the issue in general, I'm inclined to believe that a court wouldn't require states to honor the marriage policy of another state.