That's probably it.
But I also think many, or even most of these Bible-thumping zealots really believe that gay marriage is a serious affront to God, and that allowing it to become law would amount to "letting Satan lead us astray, with dire consequences for the nation", or some such nonsense. Many of these "fundamentalist" types can't grasp the concept of settling accounts with God individually versus collectively, it seems.
I wonder if they would be satisfied if we just called it something different, like "civil union". Anyway.
"Universal health care"?? What? Don't tell me you're turning into some sort of commie socialist here...