There are many arguments for and against helmet laws.  There are safety concerns.  There are liability concerns.  There are those who say that it is a bikers' right to choose.  Michigan's law currently requires all riders to wear a helmet, but that may be about to change. reports:

Two bills repealing the state’s helmet law have been introduced in the state Legislature.

House Bill 4608, sponsored originally by Peter Pettalia, R-Presque Isle, and co-sponsored by Rep. Kenneth Horn, R-Frankenmuth, would allow riders 21 or older to go without helmets if they carry at least $20,000 in personal liability insurance.

Senate Bill 291, sponsored by Sen. Phillip Pavlov, R-St. Clair, would not require helmets on riders 20 or older if they have passed a safety course or carried a motorcycle endorsement the previous two years.

Former Governor Granholm vetoed similar bills twice.  Governor Snyder's stance is unclear.