Because I grew up in a bible-based, legalistic environment and I see the same thing from conservatives and right-wingers. I hated it, black-and-white thinking is not a good way to govern anyone. That experience made me wary of anything that resembles it. My values are basically this: do unto others and stay out of people's personal decisions when they don't infringe on the rights of others. What appealed to me in that religion though was the idea of worldwide brotherhood, God accepting all people, and Jesus showing compassion for the ones who were thought of as the worst. I don't see that from right-wingers at all, and a lot of what I hear from them reminds me of the GB.
Maybe it's just that we think differently though. I'll have to dig it up, but I once read an article that explored that. You might like it too.
ETA It's Jonathan Haidt, ever read his stuff? Morals Authority