The major backlash would only occur in states that are already intensely homophobic and are probably decades away from legalizing gay marriage. There's no reason why homosexuals should have to wait that long.
The abortion similarity is a nonstarter because no one's getting killed when two people of the same sex get married. People tend to get really worked up when someone, especially a baby, appears to be getting unjustly murdered. Gay marriage...eh, they'll get over it. Even if they don't, it's not as though many young people are going to say, "I was morally in favor of the right of anyone of any sexual orientation to get married to anyone else they want, but since the Supreme Court ruled in favor of it I'm now totally opposed to it!"
Lol, I'm sure there are some white Southerners saying this. I suspect the real reason for the virulence of racism in the south was because black Americans made up such a large, and potentially threatening, minority. It's similar to how apartheid came into existence in South Africa.