[matoro]

Tumblr's tagging system is quite similar to this - you can "follow" tags or "blacklist" them and most people do tag pretty extensively - and it allows people to get away with some things that would be banned on twitter, like gore blogs. On the other hand, Twitter allows nudity, while Tumblr does not, and they both still ban for "hate speech."

[keiferski]

Right, it seems pretty implementable from a technical perspective. The hard part is having a company put I disagree with what you say, but will defend your right to say it in their company philosophy.