I've got right at 300,000 miles on motorcycles and you will never catch me on a bike without a helmet. When I started riding in the early 60's nobody wore a helmet, the shop down here didn't even carry helmets. In 1968 we had a helmet law for under 18, and my thinking was that since I was over 18, I didn't need no stinkin helmet! I might get one and wear it on the highway, but I don't need one around town. That was stupid, you are far more likely to get into an accident around town than on the highway, but accidents on the highway are much more severe.
Anyway, in 68 I was hit head on by a drunk in a Chevy Impala, I went completely over the car and landed in the gutter, on my shoulder, I only had a small bump on my head. Thinking about it made me realize that a slight shift in my impact point, head instead of shoulder, I would have been dead or seriously brain damaged rather than treated and released, I've worn a helmet ever since. I see too many people getting killed in low speed accidents where if they had been wearing helmets they would have only had minor injuries, I've seen a couple of reports of zero speed accidents where the riders were killed by simply falling off their bikes while stopped! Very simply, it is stupid not to wear a helmet when riding a motorcycle, there is too much evidence that helmets save lives to ignore that fact.
In 2005 I had my second accident, I was wearing a helmet, I had no head injury but would have suffered one if not wearing a helmet, instead of head injuries I was treated and released, which is what often happens when wearing a helmet.