But there are exceptions. For instance Perverted Justice founder Xavier Von Erk has repeatedly made it clear that he's out to punish perverts, not protect children. Also that he doesn't even particularly like children, but does dislike men.

But I'm sure even among PJ members there are people with more noble, if misplaced intentions. I have visited their forums and they weren't quite the sociopaths I imagined. When they're off the topic of pedophilia (and they do have an off-topic area) they seem normal enough, though perhaps a bit red-neck.

So you're quite right about knowing your enemies. But I guess most people are too sure they're right (or afraid they're not?) to listen to what they other side has to say at all.