This.
"I could be running a commercial Bitcoin child porn/warez/terrorist/money laundering service right now and nobody would know. Or you could be. That's the beauty of Tor. There is no way to know, and no way to shut down an .onion short of overloading it with traffic, which is much harder than with a publicly known Internet server. Well, you could of course also hack into the server through some exploit in the Web server, take over the private key and stuff like that, but that's almost too obvious to even mention and nothing that happens if the owner is competent."
-Kimmo Alm(Edited 29 seconds later.)