There are reams of cases concerning that clause, and precedent is clearly set that while minor procedural differences shouldn't be a bar to full faith and credit, substantive ones are. There are substantial differences between what one must do for a concealed carry permit in different states, not simply a case of filling out form TX738 instead of NY9245a (form numbers made up for this example). I'd point out the
Loving case centered on whether Virginia could refuse to recognize an interracial marriage, not whether they could refuse to recognize an out-of-state marriage.
Or perhaps I'm wrong about you and you believe that once Massachusetts extended marriage to include same-sex couples in 2004, all one then needed to do if you wanted to be in a legally recognized same-sex marriage in any State was get a Massachusetts marriage?
Federalism isn't about the lowest common denominator.