Not court, regulation. Wanna be a carrier? Then don't meddle with traffic. Otherwise, you are liable for all the child porn and drug trade that happen to cross your boundary.

am i a carrier when i host my own wifi network?

Right, we actually agree on this. And where is regulation enforced? In courts. Who says the provider is liable? A court. This was my point: not locking your house means a lot of processing to get back to the place where you have been before - if it can ever happen. And I'd very much not go through a whole trial...