I can't stop thinking about terrible things. ?

Namely pedophiles and rapists. It all started when I was just browsing encyclopedia Dramatica, just for minor laughs and entertainment, as my friend recommended the site to me. Little did I know what I would come to. I started coming to some really scary and terrible things, like pedophiles and raping infants. I was really horrified by it, and I promptly left the site and did not think about it again. But the other day, out of the blue, for no particular reason, I was sitting in cl and I started thinking about rapists. About really disturbing crap that were variations of a horrible image and text on the site. It got worse today, and I began feeling like I'm the worst human being on the planet just for thinking about this stuff. I feel like absolute s, as if I had done these things myself, and that I deserve terrible punishment for even thinking these things. I nearly broke down in the middle of cl over it. Please, can anybody help me in understanding why I am like this, and how I could stop? I've never been like this before, and it is driving me insane.