People should be allowed not to wear a seatbelt, but their insurance companies should also be allowed to double their premium.
Precisely, let the market forces determine the price one is willing to pay for whatever they want to do.
"...but their insurance companies should also be allowed to double their premium."
WRONG! Wearing or not wearing a seatbelt does not affect the chances of my having an accident. Therefore it should not affect my insurance premium. The insurance I pay for does not provide medical coverage for me if I am at fault in an accident. Whether I wear or not has zero-cost effect on the insurance company.