In the Netherlands you're either a tourist or 60 year or older if you wear a helmet. But it is also not that fair to compare the Netherlands to other countries. We grew up with bicycles and our infrastructure is much better for cycling.

I suspect people don't like comparing with the Netherlands because it doesn't support their biases in this argument

It's more that the Netherlands is a substantial outlier in terms of how they accommodate cyclists, so applying their attitudes towards helmets without also being as cyclist-friendly (infrastructurally and socially) as they are is asking for trouble.

Obviously infrastructure helps a lot, but there is still the danger inherent in the fact that it's quite far from your head to the ground. I don't wear a helmet though personally, since the bike infrastructure is good in my city in Germany, at least on the routes I take

I wear a helmet every single time here in Germany and I don’t when I visit the Netherlands. Not that surprising when you consider Dutch cities have (by German standards) excellent and safe biking infrastructure and, even more important, huge numbers of cyclists. You‘ll never be overlooked between cars when you’re part of a large group on the bike lane.

Almost every racefiets rider wears one. Anyone going far or fast typically does.

Pretty much exactly the same as driving: those who put on special clothes for their vehicle use activity routinely make the helmet part of that special attire, those who operate their vehicle in plain clothes don't.

if you're doing a standard 20kmh / 12mph which is a casual pace to do on a flat elevation, have segregated, dedicated space to cycle and have a culture where everyone cycles so everyone has a "cycling mindset" then yes, you'll probably see different outcomes than one with the opposite culture.

I cycle in the UK, i wear a helmet because our cycling infra is not good, cyclists are not really protected by the police, and it's common to complain about cyclists. The attitude here is different. You're the enemy, a parasite, you're in the way of my car!