As a former Christian fundamentalist (though never a fundy), I think I might be able to shed some light on this.
God is perfect. You are not. From your birth, you were a corrupted, wretched piece of trash. How. Dare. You? You deserve to suffer. You deserve pain. And nobody inflicts pain and suffering better than God does.
But there's good news. God loves you. (I think I've made my point by now).
I sincerely hope the mentality I described does not strike any chords with some people, because it is very similar to the mentality many abuse victims develop. They allow themselves to be torn down to the point where they will accept any abuse, because hey, the abuser loves them. And if they didn't have the abuser's love, they would be nothing. The thought that the abuser demonstrates the exact opposite of love is often rationalized away. It's no coincidence that whenever someone becomes a fundamentalist/fundy, there's a good chance they were at some low point in their lives, whether financially, socially, or emotionally.
It was never really like that for me. I've had some low points. Arguably, I'm in one now. But when it began, I was in the middle of the skepticism which would lead me towards atheism. I almost wished I could believe the prayers I once said. In any case, I was a fundamentalist for most of my life because I was raised that way. God tortured people because he just had to and I accepted that. On some level, hearing creationist arguments made me cringe, but Jesus spoke of Adam, so I had to believe it. I couldn't muster the same disgust for homosexuals that I could for an axe murderer, but Jesus had the power of Hell, not me, so he was morally right, not me. I suspect that quite a few people who fit the label of fundamentalist, if they really thought about the implications of their own religion, might become very uncomfortable with it.