How screwed up can people be?

There have been a lot of stories in the news lately that upset me. People doing horrible things to children. People allowing horrible things to happen to their own children. People who just plain need to be taken out back and shot, even though it is too good for them, just because it's the fastest way to stop them from breathing the same air as good people. Even kids so screwed up that they deserve to meet the same fate as adults for the things they've done.

What the hell is wrong with people? How can anybody hurt a helpless child that way? How come nobody stopped it? Some of these crimes could not have happened without somebody ignoring what was going on. How are those guilty bystanders able to live with themselves?

This stuff makes me sick to my stomach. I have a young niece. I have friends with kids. I have young cousins. I would shoot somebody, run them over with my truck, pull them to pieces with my bare hands, whatever it took, to keep a kid safe from such evil. I'm not the only one who feels this way. I'm guessing there are many others out there who agree. So how does this happen? What kind of defect to these people have, and why was there nobody willing to protect those poor kids?