It doesn’t mandate that every state legalize same-sex marriage, it requires that every state recognize a marriage which was legal in the state in which it was solemnized, in accordance with the Full Faith & Credit Clause of the Constitution. Recognition of out of state marriages under the FF&C has been in place for decades.
Marriage is the purview of the state, not Congress. Congress can not tell a state they have to recognize a marriage they don’t agree with. Supremes will shoot it down. States are the last authority on abortion and the exact same thing will apply to marriage.
True that. And I believe it gets into underage "marriages" as well. For example, IIRC California has no minimum age for marriage as long as the parents approve (which many of the diversity-is-your-strength people in California do). Until today this meant a pedo-groom thought twice about moving with his child bride out of Commiefornia because in another state someone might try to use the state's child protection services to rescue the girl from her "marriage". This law says other states have to treat the child-bride as a bride and not a trafficking victim.
The effect is the same.
If a same sex couple gets married in a single state where it’s legal, all of the other states have to recognize it. The way it used to work (before 2015) is that states only had to recognize marriages from other states when they did not conflict with their own state laws under the principle of comity.
That should work out as well as states refusing to recognize slave property by the laws of other states.
The Full Faith and Credit clause does not apply to immoral laws.