I think the confusion is that you can't understand anyone else's point of view other than yours.
You keep saying that for people (which implies me too since i'm a person) who are not on the bike and on the bike, there is NO elevated risk. Meaning the probability of a head injury is the SAME. Which you are implying. If there is no evidence of an elevated risk, would you agree that the probability is the same?
So let's say there's no evidence of an elevated risk, then how do you explain the fact that so many people here have hit their head significantly more on the bike than anywhere else? If we are in fact so accident prone, then perhaps the rest of us should continue wearing helmets and those of you who have never experienced these freak shifts in probability (since you imply that there's no evidence of elevated risk) should just go out without wearing a helmet. Problem solved, your crusade is completed.