@Catvalente Can't speak for all bad straights, but: I was brought up as a religious conservative, and the goal was always delegitimizing gay people and advancing theocracy. Gay marriage was seen as a way for the secular world to make gains on territory we saw as "ours," and as a barrier to our goal of reversing the acceptance of gay people. We believed that our country succeeded or struggled in accordance with how much God favored us. Ergo, enforcing religious law would benefit everyone.
@Catvalente N.B.: I am not this at all anymore, I just remember what I'd been taught and what was said by the people around me. The core belief on all subjects political was that we must force people to follow what we believed was "God's law" or risk the ruin of our country. There was never a deeper rationale than that. Fundamentally, these people are not living in the real world.