The justification for state laws?

In principle, a state allows itself to prohibit a person from causing harm to themselves. This is also true for cigarettes, except that there the harm is probably not as great and direct and the demand is perhaps too strong. One can argue about where the line is drawn, of course. The justification I can see for this is that if a person causes harm to themselves, they and their family become a burden on society (medical and social care, etc.). That's why society says it's not willing to allow it. And of course there's also the fear of harming other people (if you don't wear a seatbelt and get hurt, you'll lose control of the car and maybe others will get hurt). This is the justification. As for the right to do so (and this is a different question), it is about using the resources that society puts at our disposal (roads, streets, and even cars, and of course other social services – security, education, welfare, etc.). Therefore, society can condition the use of its resources on various conditions. And above all, if you accept the perception that the person is also a member of the public collective and not just an individual, then the collective can make decisions for him (just as he makes decisions for himself).