In South Carolina, interracial marriages were illegal. Two people of different races married, they went to prison. Actually, probably just the black one.
In South Carolina, gay marriage is banned/not legally recognized. Two men or two women find a social institution to marry them, fine. They're married in their eyes and that institution's eyes. They do not get arrested and imprisoned for holding themselves out as married.
What they don't get is tax breaks for being married or access to family court in the event of disollution/divorce. South Carolina does not interfere/nullify with private contracts entered into by same sex partners.
In SC (and federally), people are raising hell, not about marriage or the right to marry, but fundamentally economic/tax/too-lazy-to-write-a-proper-will issues. If you want to put = signs up in solidarity of that or scream bloody murder about God's wrath on the gays, great, just know what the heck you're advocating for or against.
Your gay son/daughter/uncle/aunt/sister/brother/friend/self can go get married right now if someone will officiate the ceremony.
If you're in another jurisdiction and gay marriage is illegal, they by all means continue railing for/against what you've been *thinking* you're railing for/against.
(As it is always possible I have details incorrect, inadvertently, please comment and if valid, I will update)