Every sport where you participate in the open...kayaking, climbing, cycling, etc, etc...the vast majority of people wear a helmet. Wearing helmets is on the increase even in snow skiing...i wear one. I have a deep scrape mark on the front of it which would have been my forehead had I not had it on when I face planted on packed powder snow. I am no novice skier, so anyone can have an unexpected fall at any time. If I'm participating in any activity where my head is traveling at a speed faster than I can walk or run, I'm going to have a helmet on.
Any argument made to say that a helmet does not help prevent head injury in the event of impact is illogical. Proponents against helmet laws are making their arguments based on emotions and not logic. If your head hits a stationary object, even at speeds as low as 10MPH, it is going to sustain some kind of more serious injury without a helmet than with one. Period. Your brain cavity is not made to protect it's contents when an impact occurs at a greater speed than falling down from a standing position. Even then it can sustain serious injury. To propel it through space on purpose at great speed (relatively speaking) and not protect it...the odds are against you. Period.
Everytime anyone gets on a bike without a helmet....just take a moment to think about how it would feel if someone came up behind you and took a half strength swing with a baseball bat to your head...I mean, really imagine how it would feel... and whether you feel lucky today, and whether you want to ride again tomorrow.
Oh, and by the way, the second most likely part of your body to get seriously injured in a motorcycle accident is your feet (obviously your hands will be hurt if you go down)...so when you hit the starter without a helmet on, slip into those sandals as well. Then you can get matching chrome crutches to go with that plate in your head.
It's your choice though...and this is not meant in disrespect of anyone's choices here. I just care about my fellow riders.