Not forcing the helmets does not equal a freedom of choice. It merely changes the forces at work. Should helmets be required, it would be less likely for people to view you as a whimp for wearing a helmet. Or for people to think that they are being viewed as whimps for wearing helmets. Just check the history of NHL... players wearing helmets were being berated by everyone. Now they are required to wear such things during the match, and not too many would consider playing without.
Seat-belts are not your personal choice. The moment you crash your car into something heavy/immovable, you become a human cannonball.
Also +1 what Dala said.