In agreement with MickS and nightwork4, but more in response to Christopher Limm, I disagree with your idea of what the law is supposed to do.
The word "law" defined: the principles and regulations established in a community by some authority and applicable to its people, whether in the form of legislation or of custom and policies recognized and enforced by judicial decision.
The government really has no right to enact a law for this. It's just as silly as requiring people to wear seat belts in a vehicle. Sure, there are studies that show that a helmet is safer, but it should be up to the individual.
Where I do have a problem, is when low-income folks are allowed to crash cars and bicycles and anything else, but have other people pay for the damages due to lack of insurance and lack of money. That's a separate problem though - freedom should not be given to the government, they have enough to deal with that they've become inefficient at everything trying to police and enforce so many small things.