Steve Chapman of Reason magazine on why motorcycle helmets do not constitute a "public health issue," which is the argument being used by the National Transportation Safety Board in urging Congress to make them mandatory:
A public health issue arises when masses of people are exposed to illness or injury by dangers beyond their control—contaminated water, sooty air, natural disaster, marauding bands of hyenas—or when I get a serious disease that I may pass on to you against your will.
In these cases, government action is necessary. It's perfectly legitimate for governments to regulate pollution, build levees, and require people to get vaccinations.
But riding a motorcycle without a cranial cushion poses no danger to anyone except the rider. Skull fractures are not contagious. The public is not at risk if I decide to mount a Harley with nothing but a pinwheel hat on my head.
[. . .]
It's also hard to see why we single out motorcyclists for the sin of saddling everyone with higher health care costs. Plenty of patients suffer from self-inflicted ailments—lung cancer from smoking, liver damage from drinking, diabetes from eating unhealthy foods, AIDS from unprotected sex. Yet we don't ban these activities.
Why not? Because we retain a respect for individual freedom and choice—even in matters of life and death, even when individual choices have collective costs. Motorcycle helmet laws are an unwarranted exception to our normal, sound approach, which can be summarized: It's your life, and it's your funeral.
Helmets aren't being singled out, of course. The same "adding to the collective costs" argument was used to make seat belts mandatory, and the same arguments on both sides of the debate apply to that issue as well.