Com'on people. You're all biased because you all enjoyed the show. Yes, there's violence in it. Just because other shows made it through the censoring doesn't mean that those shows presence justifies elevating PR to "accepted" status, much less justify those other shows at all.
Believe it or not, visual violence does affect kids, whether it be cartoon, real people, video games, etc. You ought to know that you become like the people you hang out with/idolize, and the same is true with television. Granted, now that we are older, we have built up personalities and morals that are far harder for something or someone to alter than when we were just kids. But the fact remains that you become more tolerant of this sort of thing.
You don't have to copy people on TV and in video games to become more tolerant of the activity. The more you watch, the less you mind. This is the biggest issue. This is what happens with kids: over time, they become more tolerant of the violence and don't notice the evil within it. Surely we all recognize the evil in the violence - or at least some of us do - but we don't notice it as much. And because of that, there is less desire within us to stop that sort of activity and change things.
Now about the villain thing - I don't care if it is a villain, villains can scare kids. I have seen villains that are not so scary. But to be honest, it's about what your kid / younger sibling (in my case) can handle: some kids can put up with freakish monsters and some kids get nightmares.
However, I do wish to make an important point that I think we all agree on: if your kid can't handle it or you think it would harm them in some way, WHY ON EARTH ARE YOU CONSIDERING LETTING THEM WATCH IT?! (sorry for the yelling)