I hope no law will require wearing helmet when riding a bike. If such a law is ever proposed seriously, at least it should have the qualification such as: a helmet is required if your riding speed is over ____ (a high speed). But then it will be hard to carry the law out. So, please, no law.
Thousands of people ride bikes mainly locally for errands. It will be ridiculous to require them to put on a helmet in order to ride to the post office 5 blocks away.
Except that helmets apparently are fine for low impact falls which are associated with low speeds, and vice versa. Yes, counter-intuitive, I know.