There are good reasons for not making helmets required. See e.g. this overview: Bicycle helmets and the law, http://www.bmj.com/content/346/bmj.f3817.full http:

There are good reasons for not making helmets required. See e.g. this overview: Bicycle helmets and the law, http://www.bmj.com/content/346/bmj.f3817.full http://www.bmj.com/content/346/bmj.f3817.full