tldr; Please, if you care about the safety of bike riders then stop harrasing people over helmets and encourage more people to ride bikes. That will actually make us all safer .
Riding a bike without a helmet is better than not riding a bike at all.
Every time you harass someone about not wearing a helmet then you are increasing the likeliness that they (or someone else) will opt to just take a car somewhere instead.
Shaming people into changing their behavior doesn't work. Polite society generally don't accept this approach in other areas of life so why do you find it acceptable here?
Oh, did an ER doctor tell you about how many brain injuries they see from injured cyclists?
There's definitely no selection bias going on on their part. A nice double whammy of confirmation bias on your part, too.