This is a very hot topic as of lately. Like many issues that are best left not being political (ie, abortion), I think the issue comes down to your personal comfort level.
The main argument against a helmet law goes something like this, the amount of protection it provides is minimal and the physical/environmental benefits of riding far outweighs the risk of not using a helmet. In fact riding a bike is as safe as walking, mile for mile. So the effect of a helmet law would could have a chilling effect on the number of people riding. Accordingly, we would be better off with a few more injuries/casualties and significant less physical ailments/deaths due to lack of exercise.
The argument for a helmet law, is similar to the law for wearing seat belts. Accidents WILL happen and the helmet WILL provide critical protection to some. In addition, the public will not be forced to pay for the medical bills of the uninsured bicycle rider injured by not wearing a helmet.
For a free legal consultation,
I do not believe there is a right answer in this debate. My personal beliefs are that there should be a helmet law, however, it should only be applicable to persons who do not have health insurance. Here is some more information on bicycle accident statistics.