It's proper that the government raise an armed force to defend the citizens against agression from a foreign government.
Aside from the logical reach someone has already brought up here, that you might injure an innocent bystander if your body is ejected from your vehicle, you pose no hazard to anyone by opting not to wear a seat belt. That issue is what determines if this is an appropriate area for government involvement.
I agree with everything you said, I really do, but I'm just of the opinion that in an ordered society, sometimes there are exceptions for the common good.....like underage drinking, littering blah blah blah......who decides these exceptions is something though I would look very carefully at.....
I hate to quote "Analyze This" but, "You're good, you!"
I've written about two posts already that you beat me to the punch with almost identical responses.