A lot of people get really dogmatic about safety gear in very specific ways.

I'm willing to bet that a lot of the same people who think that not wearing a bike helmet (and especially allowing a child not to wear one) should be a criminal offense would think the idea of having to wear a helmet driving is just silly.

The attitudes around helmets for downhill skiing have gone through a similar shift. It used to be that essentially no one except racers (and then snowboarders) wore helmets. Now, at least some people will chastise you if you don't.

And it's not just a US thing. Copenhagen and Amsterdam are both big bicycling cities but a fair number of people in Copenhagen do wear helmets and you don't see nearly as many of the bare headed young kids perched on top of the handlebars that you see in Amsterdam.