I've personally never understood the need for religion to get involved with issues of the State anyway, and I don't think blatant bigotry is the reason, and I also think its [bigotry] an oversimplification of the issue. Maybe believers and non-believers need to understand each other better instead of tossing around lazy-brained labels. I think people on the left are much more guilty of simply trying to label someone.
I think that religion simply believes it has a personal obligation to legislate its morality....this goes back probably as far as the Roman Empire, in my opinion. This is not about bigotry, or "supporting slavery", as some small-minded intolerant people say -- this is likely about them feeling as if they're ordained and commanded by God to reform society and restore a sense of morality in the world.
Most religious people I've personally talked to feel this way...that they need to put God back into, what they see as a "Godless world". These people are sincere, and honestly think they should use whatever means necessary to restore God into society.
This is an unbalanced view, in my opinion, but its the reason why I think "red states" fight back against "equal rights".