musing on sandy hook

i spent most of last night awake, thinking about this. i have a really visceral reaction to children being abused so i'm not surprised.
i still can't quite get my mind around this, it's sort of like my reaction to the 9/11 disaster. i didn't watch the coverage because i didn't want to see it. i still can't comprehend it.
i've spent a portion of my life in social service jobs so i'm well aware of what people do to each other. i'm rarely surprised at the depths some people go to and i could relate my fair share of horror stories from those years but i've always retained the anne frank outlook that at heart i believe most people are basically good. so what happened here?
the shooter used guns registered to his mother, they were legal and he apparently he didn't spend a great deal of time planning this. he was socially awkward and not the least bit violent in the past, if anything, people around him were afraid that he'd be bullied. is it a comment on our society and our media entertainment that someone would suddenly think this is in any way acceptable?
i grew up on the weekly crime and cowboy tv shows. i loved the clint eastwood movies. to this day, when i want mindless entertainment that doesn't require thought i look for some action movie that i haven't seen but that promises a lot of shooting, blowing things up and basic destruction. and i also spent a part of my life in a job where i carried a gun every day. i hated it. to the amusement of my co-workers, i kept it unloaded because i couldn't stand knowing that it could be fired at someone. i had already made the decision that under no circumstances would i ever fire it at anything except the yearly targets for cetification.
i also grew up with a realistic view of what the world was like. one of my very early memories involves television. in the early days, tv stations used anything to fill up the off hours of their schedule. when i was 4 or 5, i used to get up early, at sunrise, get out of bed and go downstairs and turn on the tv to wait for "ding dong school" and "captain kangaroo". the local station filled the space with old newsreels before the network programming. i still remember seeing the newsreels of concentration camps and the piles of dead. my mother had to explain to me what a concentration camp was and how all of those people died. my father had died a little while before and i couldn't equate him, lying in a suit in a pretty box in a pretty room with those piles of abused corpses. adolf hitler was the devil incarnate, we all knew that and he gave a real and remote face to evil...but the good guys won!
i'm at a loss. i've never believed in the principle of pure evil. i'm questioning my naivete at this late date. is there some force at work in the world that creates an adolf hitler or the 9/11 murderers or a socially awkward kid who suddenly becomes a mass killer for unfathomable reasons, no matter what we do? i don't want to believe it's true. if it is, maybe the best thing we can all do is pray that the world really does end next week. i'm tired of living here.