No, seatbelt laws are to save the people in the car mainly, but it’s worth noting that it’s not just a matter of not wearing a seatbelt being less safe for yourself, it’s less safe for others because you being much more likely to die or be seriously injured means you are much more likely to not be able to help other people who have a chance of surviving in an accident.

That said, I also think it’s perfectly fine for the state to demand that you don’t just recklessly endanger your own life like that because it’s a trivial psychopathological “benefit” for contrarian libertarian types at the expense of literally everyone and everything else to have more people dying and seriously injured at any given time.

But I was also caught between that and your examples of assault and I can see why you’d find it unclear.