80%+ of severe injury and death on a bicycle is caused by motor vehicles, or complications of motor vehicle involvement.

Which would mean ~1 in 5 have absolutely nothing to do with a motor vehicle. That’s significant.

There is considerable evidence that everyone wearing a helmet in a car would save vastly more lives and prevent severe head injury

Then that should be an easy [citation needed] for you because my searches are coming up blank for actual studies. Lots of assertions of it, but I’m not finding anything in terms of actual data.

It’s very easy, on the other hand, to find comprehensive meta analyses on the efficacy of helmet use.

It’s also worth noting that the introduction makes a point of calling out another common online assertion that you repeated – that helmets make people engage in more risk-taking behavior – as false:

There has already been an extensive peer-reviewed literature review conducted by Esmaeilikia et al.5, which found little to no support for increased risk-taking when cyclists use helmets and if anything, they cycled with more caution.

I don’t feel those people should be called stupid for their choice.

I don’t think they’re stupid. I think they’re bad at risk analysis. That’s a pretty inherent feature of humans. It’s the reason I want to see actual data.

A helmet is only needed if you intend to spend significant time in traffic.

The worst wreck I’ve ever had on a bike was without a single car in sight. Pinch flat while carrying speed through a steep downhill curve. I split an expensive MIPS helmet in two and still hit hard enough that I had a minor concussion, road rash up one side of my body, and cracked the face of a week old watch just to pour salt in the (metaphorical) wound. I mostly landed on my head and that helmet is the reason I didn’t have drastically more severe head injuries.

Helmets aren’t just for traffic.

This comment is kind of fascinating because it’s essentially reinventing Slashdot’s metamoderation system 25 years later.

It was good then. No reason it wouldn’t work again today.

I was familiar with Overthrust from Botswana just to the north because Vice did an amazing article on them years ago (that fortunately has been captured by the Wayback Machine since the photos are gone on the live site):

https://web.archive.org/web/20201024232145/https://www.vice.com/en/article/3b5pp3/atlas-hoods-botswanas-cowboy-metalheads

African. Cowboy. Death metal.

I used to follow them on Facebook back before I ditched social media. Their aesthetic and commitment to the bit is fucking fantastic.