I do not wear a helmet and my state does not require it for people over 18. I find the wind blowing in my face to be much of the fun of motorcycle riding. I enjoy the sights and smells, and a helmet limits that to some extent. I fully support making it the choice of the rider. Some people prefer a helmet because it does offer protection in many cases. On the flipside, I was once run off the road with no helmet, and the extent of injuries to my head were a cut over my eye and on my earlobe. A helmet may have restricted the motion of my head and caused damage to my neck as I tumbled over. So... to each his own.
On a side note, I know somebody who was competing in a mountain biking race wearing a helmet, and he suffered a bad spill, broke his neck, ribs and suffered such a severe concussion that he is now brain dead. So helmets are no GUARANTEE against injury. They can help in many situations, but motorcycle riding has some inherent dangers. For those who are very safety conscience, you might want to think twice if riding a motorized cycle with little bodily protection in traffic is the right choice for you.
That's my .02.