No, they shouldn't. Do I think it wise to not wear a safety belt? Certainly not. I do, however, feel that putting your own health/life at risk is your business, it's a matter of personal freedom.
Some insurance companies (where legally available) offer motorcyclists a "ride free, for a fee" policy, which allows them to ride without a helmet at a slight increase in cost. This could, and I think should, also apply to people who don't wish to wear a seat-belt.