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.
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...