Whislt I'm not in favour of compulsion either, I must clarify the following point:
The whole point of the helmet is that the decelleration forces between brain and skull are lower because some of the force is dissipated by the helmet, much like crumple zones prevent the full force of impact being transferred to the passenger cell in a car.
I have also read that brain injury results from the brain hitting against the inside of the skull, so wearing a helmet would not make any diffrence to this.
The whole point of the helmet is that the decelleration forces between brain and skull are lower because some of the force is dissipated by the helmet, much like crumple zones prevent the full force of impact being transferred to the passenger cell in a car.