Governments try to shut down sites, but that's the most they can do. I think it was the NSA who created TOR in the first place. There would be serious backlash if they stopped people from using that because in countries where censorship has gone wild, TOR is the only kind of freedom that people there can have. Also, there are some theories that suggest that certain governments have servers so they can essentially spy on paedos and whatnot. Furthermore, people high up in the government are corrupt anyway. God knows their own paedos use TOR themselves so even if they could shut down the websites or TOR itself, they wouldn't because they'd lose out.
While we're kind of on the subject, watch Eye Candy. Or don't if what you already know freaks you out too much.