http://en.wikipedia.org/wiki/Ignorantia_juris_non_excusat
In the case of uber you might attempt to make the case that uber is enabling/encouraging/paying people to break the law. That is illegal by itself.
My point was that if AirBnB did anything which limited itself to operating in legal areas, it would be several orders of magnitude smaller.
http://en.wikipedia.org/wiki/Ignorantia_juris_non_excusat
In the case of uber you might attempt to make the case that uber is enabling/encouraging/paying people to break the law. That is illegal by itself.