The problem with your theory is that if these people really had a problem with "sin" per se, they wouldn't have held their noses and voted for Trump.
Some of these folks don't like the idea of the world being different than the one they grew up in. Others don't want their kids growing up in a world that's different than the one they grew up in. You've also got the control freak weirdos who don't even have kids but hate the idea of other people's kids growing up in a world that's different from the one they grew up in.
Lastly, you've got some folks who just really find the concept of two people of the same sex getting freaky with each other to be disgusting. It's like if you knew your neighbor was beating puppies to death in his house, that'd probably bother you, right? Well, now imagine you've got some weird irrational miswiring in your brain that puts gay sex on the same level as beating puppies to death. Those are the people you just have to wait for them to age out of society before their homophobia finally goes away.