During the Jim Crow Era there were a lot of unconstitutional things going on. Plessey V. Fergueson allowed a lot of blatant ignoring of the equal protection clause.
You also have hall the differences in ages of consent, as well as first cousin marriage allowances between states, and you don't have them ignoring marriage certificates that don't meet their own requirements, they just won't issue their own unless you meet their requirements.
There are a lot of unconstitutional things going on today. That isnt an argument.
Obviously the differences in consent etc are not major enough for states to object to other states' standards. That would be the case here.
I don't think then content matters as much as the process. If a State uses its legislative power to change the marriage contract to include same sex couples, I can't see how another State can say "we won't recognize it" without violating the full faith and credit clause.
And I agree that a lot of unconstitutional things are going on today, however those of us who believe in strict construction can't throw it out the window (the way progressives do) when it doesn't suit us.
I would hope a Full Faith and Credit ruling in this case would also bolster cross-state CCW permitting.