Even if the state doesn't pay their medical bills or provide any other assistance to the person not wearing their seatbelt you will be affected.
Some percent of the adults driving who are killed or disabled in this manner are going to leave behind kids who are emotionally scarred because of the loss of a parent. These kids become the so called "at risk" kids because of the double whammy that not only have they loss a parent, but they effectively lose both because the load on the other parent is now so heavily increased. If not dealt with, the "at risk" kids tend to turn to crime.
And that crime will cost you. Either they will steal your stuff, a direct cost. Or you will pay taxes to have them locked up in the penn., or you will pay for security or additional cops.
That guy won't pay his last utility bill (so the utility company increases their rate to all their customers including you), he can't pay his mortgage, so the bank raises the interest rates they charge all new customers, he can't pay anything and every business will have to build in a small cushion and charge you, so that they can pay for Joe when Joe crashes without a seatbelt.
Your inattention to provide for the common welfare in the beginning will come home to roost in more ways than you can imagine.
By the way, suppose you are robbed and they take you to the emergency room. Your ID is stolen, so the hospital refuses to aid you because you can't prove your ability to pay them. Is that really the kind of world you want?
If your theory were followed to its logical conclusion, there would be literally no human activity that would go unregulated. Every single thing we do entails some personal risk, from crossing the street to cooking dinner.
Where would this regulation end? Theoretically it could go on forever, until people were fed only gruel (you might choke on solid food!) and confined to padded rooms and strait jackets (most accidents happen in the home!), released only long enough to complete jobs that were justified by a risk/benefit analysis of be of sufficient benefit to others.
You also assume that you have some right to the benefits of others existence and their work. You have no such right. People are not cattle whose liberty depends on how much they benefit others. If I die today in a parachuting accident, or even decide to take my own life (it is mine after all) and that causes you to miss out on something I might have done to benefit you, well, Tough.
Your theory is that of slavery. Not slavery to an individual, but slavery to everyone. I am no man's slave. If you benefit from my wellness, consider yourself lucky. You have no right to the least of the fruit of my labors, unless we agree to it beforehand. If my demise causes some creditor of mine a loss, that's simply the cost of doing business in a free society. The free market system, through the 'Invisible Hand' will handle that.
Freedom is not free. It costs more than lives spent on a battlefield or trillions of dollars spent on 'defense'. Freedom is not neat or orderly. How much of a mess do wars we supposedly fight for freedom make? All those costs are merely a minor portion of liberty's cost. The consequences of my right to be as reckless with myself as I wish, so long as your rights are not violated are part of that cost.
suppose you are robbed and they take you to the emergency room. Your ID is stolen, so the hospital refuses to aid you because you can't prove your ability to pay them. Is that really the kind of world you want?
I can solve that problem real easy: In exchange for treatment in that case you agree to be photographed and leave a thumbprint with the hospital (now your creditor) in lieu of conventional ID. In the event that you don't pay, your thumbprint and photo are given to the police as evidence of breach of contract. If your thumbprint is not on record and you cannot be found and prosecuted, your picture and thumbprint are shared with other hospitals much in the way casinos share information on undesirables, and you can be assured you will not steal treatment in the future. The cost of this system and losses from those that don't pay are offset by an additional fee on those customers who use the system.
Nearly every problem such as this can be solved with voluntary solutions. All it takes is thought and effort.