I agree, someone not wearing a seatbelt can, potentially, become a hazard to others.

But is it often enough to give a shit about? In a two minute search, I found no statistics about "human projectiles" causing harm, which to me means that it is not a significant factor in accidents; otherwise pro-seat belt lobbies would have something on it.

I'm a realist, and a cold statistician when it comes to shit likes this: Yes, people may die, get injured, or otherwise be hurt by shit. They always will. But unless it is a significant risk? I feel it should not have bearing in the discussion of restricting the rights, and freedoms of the people.