From the AMA (99%ers)

Washington, D.C.: A new recommendation for universal motorcycle helmet laws by a task force of the U.S. Centers for Disease Control and Prevention is based on faulty reasoning, American Motorcyclist Association reports.
The Community Preventive Services Task Force recommendation is based on studies of U.S. states and foreign countries that require all riders to wear helmets, those that require only minors to wear helmets and those that have no helmet requirement. The CDC task force produced no study of its own and cited no detailed analysis of crashes and fatalities to adequately assess the role of helmet laws in preventing serious injury or death in crashes. Instead, task force members merely looked at other studies and drew a generalized conclusion.
The AMA has long advocated the voluntary use of helmets, but opposes mandates because helmets do nothing to reduce the likelihood of a crash.
The AMA strongly encourages the use of personal protective equipment, including gloves, sturdy footwear and a properly fitted motorcycle helmet certified by its manufacturer to meet the DOT standard. However, adults should have the right to voluntarily decide when to wear a helmet. The AMA does not oppose laws requiring helmets for minor motorcycle operators and passengers.
A complete statement of the AMA's position on universal mandatory helmet laws can be found here: www.americanmotorcyclist.com/Rights/PositionStatements/VoluntaryHelmetUse.aspx.