Seat belts are another matter. you can be fined for not wearing them. Of course, you can also be dead, but no one seems to worry about that.
Laws aimed at making people healthier or preventing injuries and death can only be justified if poor health and bodily injury impacts people who weren't in on the decision to smoke or not buckle up. Impacts, for example, like higher premiums for health care, or more taxes for same. Were we willing to simply allow the unbelted driver die beside the road, then we would have no justification for requiring seat belts.
But, then, most of us don't want to live in such a society.