From the FAQ:

  Do you really expect to be able to detect and 
  filter anything that's conceivably stupid?

    No, of course not. You'd need real AI for that, 
    and beyond a certain point it's simply subjective; 
    after all, a sufficiently advanced AI would probably 
    filter out the whole of human discourse, which 
    isn't the idea.

I have to admit that I laughed pretty hard when I read that...