That's because the scale and untracked nature of such noncensored sites make their impact difficult to quantify. We know that social contagions exist, but we don't know the extent to which they affect people.

School shootings are far, far more common than they used to be. They started to really rise around the same time that sites like 4chan glorified the shooters and discussed the issue like it was a game. They spoke of becoming an hero(sic), talked of getting a high score, and made memes of their dead bodies.

The world tends to loathe extremes. We know that extreme censorship causes social issues. Why wouldn't complete non-censorship combined with anonymity cause issues too?