> Seat belts work. Use them. Those won't don't use decimate themselves over time. E.g in Austria of the 178 car occupants killed last year 42 didn't wear a seat belt[0]. Those 23% is far above the 8% that did not use a seat belt in observations[1]. Numbers for other countries are similar or worse.

Why not let these people decimate themselves?

Tempting. But we already have an aging population, let’s try not to get too many reckless young people killed.

Or: a law to reduce the amount of accidental deaths seems like something good for the population in general.

Ask your parents, spouse, children, co-workers how they'd feel if you died simply because you were to lazy to do just one simple action before driving off into the sunset. I'm pretty sure they don't want you to join the Derek Kieper club https://www.snopes.com/fact-check/seat-belt-advocate-killed/