I'm afraid the Union Army wasn't fighting for gay rights, so I don't quite see how that applies. Nor do I see the relevance of your curious implication that because I question the appropriateness of the Supreme Court proclaiming gay marriage by fiat, I must also be interested in bringing back slavery. ("Maybe the Thirteenth too while you're at it.")
Of course not. But that is, sadly, not an option. The forces of ignorance and bigotry are too deeply entrenched in the U.S. That is one of the costs of freedom. People are free to be ignorant, and they are free to be bigots. But the government -- neither federal nor state -- does not have that freedom, thank God.
> I'm afraid the Union Army wasn't fighting for gay rights,
No, they were fighting for the union. But then, having won the war and established the nation as a sovereign power, when the fourteenth amendment was duly enacted it became binding on all the states. Sometimes when you fight for things you end up accomplishing more than you set out to do.
Ultimately, the Supreme Court, by virtue of the fact that the Union army won the civil war.
If you don't like it, you can always try to get the Fourteenth Amendment repealed. Maybe the Thirteenth too while you're at it. Good luck with that.