I believe everyone should wear a seatbelt, but I don't believe it's the government's job to legislate it.
I've heard stories about people who died in accidents even though they had seatbelts on, and I've heard the stories about people who would have died if they had been wearing a seatbelt instead of being thrown clear. That being said, in all my years as a paramedic, I never once had to cut a seatbelt off to remove a body from a vehicle, but I've lost count of the number of times I've found dead bodies under cars, on their hoods, 100 feet from their cars, run over by passing traffic after they were thrown from their cars, etc...
I feel the same way about helmet laws. I think you would have to be crazy to get on a motorcycle without a helmet, but I don't think the government should legislate it.
I didn't always think helmets were necessary. Then I went over the handlebars of my motorcycle at 70 mph without a helmet. I basically walked away from the crash (thank you God!) but my injuries (fractured skull, fractured orbital bone, broken nose) would have been a lot more minor if I had been wearing a helmet.