You want to wear a helmet. The risk-reward ratio is highly in favor of wearing one. What is the burden of wearing one vs. having some protection in case you fly?
Why don’t we do that? Because while the burden is low - it’s mostly dragging the helmet around wherever you go and ruining your hardcut - the actual probability it might help is quite low. And with good infrastructure, the same is true for cycling. If you look at this years stats for causes of death for cyclists in Berlin for example, the leading cause is “crushed by a truck”.
Note: if you do cycling for sports at high speeds or rough terrain: wear a helmet.
Edit: To be clear, I was riding years without a helmet until a crash made me reconsider my priorities. Also, I am not in favor of mandating helmet usage on bikes.
All kinds of race car drivers were helmets - and their steel cages are much much more sturdy than the ones that commuters have. Statistics als indicate that many car drivers suffer head injuries. So by all available evidence, wearing a helmet in a car is not redundant. Still, people don’t do it - unless they engage in particularly dangerous activities.
The parent poster that you refer to explicitly gave his speed as about 20km/h for commuting, which is neither particularly fast nor particularly dangerous on good infrastructure. So why wear a helmet?
For me this discussion is done. I have this particular perception, you have yours. We are both happy with it. Stay safe.
I understand fear of someone who actually was in one, but please stop forcing your fear on everybody else. Just because you are afraid does not mean not being afraid is irresponsible or any more irresponsible then not having helmet in car crash.