What exactly, are these "staggering costs" we pay for unhelmeted riders?
Check with the family of someone who has had a stroke or brain injury, who was the principle breadwinner for that family and you will see what those staggering costs are.
If the brain injured person is in their 20-30s, no amount of insurance on the planet is going to pay for their care and upkeep for the next 40-50 years as they need 24/7 care.
If that family has kids, and the odds are they do, then at some point, if mama has to go back to work, hired help has to take care of the brain injured spouse. If you don't think the government starts picking up the tab at some point, you just don't understand family economics. On another thread I just posted up a chart where 83% of all families in the US have UNDER $250K in available savings according to BLS. 24/7 care will piss $250K away in under six months.
You can reset pretty much any bone in your body but shoveling the little synapses and gray cells back in your skull in the correct order is a real bitch. I have been a rider since 1966 and I would not be on a bike without a helmet.
For simple evidence, just look at Gary Busey, he hit a curb at 5 MPH
without a helmet. He has spent over $5Million in medical bills to get where he is today.