So if a cab gets in an accident, then the person who hail'd the cab should be liable? What if it is an autonomous cab? If an automated elevator fails and kills someone, is the person that pushed the call button liable?

This is something that I really don't like about our society, the fact that someone "must" take be responsible. When someone goes on a shooting spree, of course they should go to jail. But if they die in the process of committing their crime, there is almost always an outcry for the next person in line to be responsible.