Well, obviously because they're evil. duh.
It's a bit more complex than that.
IMHO, a lot of people leave the church because they don't feel comfortable there. They hurt in the very place where they want to feel healing. And the hurt overpowers the opportunity for healing.
It's hard not to judge. We do it constantly. And we often judge unrighteous judgments.
And when there is a cultural and political conservatism imposed where it need not be, it can create insurmountable conflict.
Yes, I'm speaking of the "wink, with, nudge, nudge" crowd who are so anxious for the world to be evil as they point it out so that they can rejoice when the wicked are punished and they are proven right.
Anonymous D gave me some insight recently that this kind of prideful thinking is very much the "Nephite Disease" of the Book of Mormon. It is in classifying people with whom we disagree as the "other" and relegating them to a level of righteousness and eternal judgment much lower than our own. If they're not with us, they must be against us and likely Lamanites to boot!