He isn't saying people shouldn't wear a seatbelt. He's saying it should be their choice. If someone chooses not to wear their seatbelt, they obviously care more about their own convenience and comfort than their safety and well-being. Why should he (or anyone else) worry about their lives more than they do themselves?
Not to sound harsh, but I think that your logic epitomizes the stereotype of the extreme liberal who thinks it's everyone else's responsibility to support and take care of you. You've alienated anyone who doesn't have a strictly socialist view of the world.
Of course, if you're not alienating someone, then you're probably not thinking things through enough to form a strong opinion. So, good on you for having an opinion either way ;-)
When I realized that allowing this freedom could possibly encroach on my freedoms, it became a different issue. And I changed my mind.
The case for wearing a seat belt is my exception to this rule. I was talking to a "libertarian" friend and he mentioned his life is his responsibility and he should wear the seat belt or not if he didn't want to. I told him that if he got in an accident and paralyzed because of not wearing seat belt then it wouldn't be fair to the rest of us tax payers to support him because of his decision. (This was in a modern country with universal health care).
He thought for a second and said, "oh, yes, you're right".
Luckily, I live in a no-fault state though. But still, that's a very good point.
I'm glad I'm not a libertarian or I'd be experiencing cognitive dissonance.