I think people engaged in those kinds of activities cannot be killed or injured by another person.
The problem with seat belts is that if someone is not wearing them, they can be hurt by someon else (and then they can sue).
People get hurt with seatbelts as well, that's not a valid argument.
The truth is the people in the back seat are the one's that should be required to wear them, some countries do because of the head/neck injuries sustained by front seat passengers during collisions.