FWIW,
I used to get asked at times by bikers why I didn't tell them they should wear a helmet. I figured they knew the price of their head and if they didn't think it was worth more than a helet I didn't either. Unless they were under 18, that was mandatory by law. Another reason was one of the major trauma hospitals in town was also the transplant center. There are lots of folks who could use the parts.
Personally I think that seatbelts should be similar to helmets and that both should be grounds for loss of coverage for insurance. Not liability, just coverage for your loss and injuries. Harvesting could be done for transplants and the state should not be obligated for "heroic" measures to maintain a vegetable if they were not using a belt or helmet. Organs tend to drop in ability to be used for transplants after a while on life support, so once that time has passed, pull the plug. But that is just my cynical feeling after having responded to more than a few collisions. For those under 18 the state still has an obligation to be responsible for your "welfare" so helmets and belts would be mandatory for juviniles.