Sorry if this sounds harsh, but people who work in ER have skewed opinions because they’re only dealing with the people who end up with serious injuries.
You need to look at the bigger picture - first of all what’s the probability of having an accident, then within that probability what’s the difference between wearing a helmet or not. That then needs to be compared against the risks of staying sedentary. It’s complicated.
Of course the have their biases, but they actually only ones who see the cases mostly not covered in statistics and they are the ones who can say whether helmet would save someone or not. The problem is that our culture is biased against fatalities. Even in this discussion there are mostly links to graphs about death rates. But these people in ER are the ones who see a lot of cases where death would be better outcome. Looking at my neighbours taking care of almost completely paralyzed son (accident not related to transport), I tend to agree.
You need to look at the bigger picture - first of all what’s the probability of having an accident, then within that probability what’s the difference between wearing a helmet or not. That then needs to be compared against the risks of staying sedentary. It’s complicated.