Well - that's the curse of the decentralized idea. There is no control, which means also no control over evil. I also flagged child pornography once. It was a really disturbing experience. But we are all responsible for what we do.
When a child has unlimited access to internet, it will get spammed with pornography. The web is full of it. Why should it be different here? There is good and there is bad - two sides of one medal.