Okay, let's talk about helmets for driving, and let's get personal. You don't see professional race car drivers going helmetless in races. I wonder why?
In the 1970's, I was involved in a head-on auto accident. Shortly after that, I decided to drive in some stretches of highway with my motorcycle helmet on. I reasoned that I wore a helmet while crewing an Air Force helicopter, and the impacts were about the same as a helicopter crash from an engine-out autorotation. After a while, I stopped that, but it was a reasonable reaction to my accident. I've had three auto accidents of significance, and no head injury (although seat belts saved the day on one, and I always wear the seat belt).
I've also had three bicycle accidents of significance. As a kid, I fell off a bicycle going home for lunch, and smacked the side of my head on the pavement--no helmet, and the start of life-long migraine headaches. Last May's accident was my last one. I've said it on other threads (and perhaps here too, above, a while back); the doc said that, if I had been unlucky that day in May, 2002, I would have lived without a helmet. With a helmet (now in more than ten pieces), I have recovered fully, and can type this reply.
Those of you who continue to bicycle without a helmet are in denial--the "it cannot happen to me" syndrome. It can! Ask whether you and your family would benifit from the minor inconvience of wearing a helmet if there was an accident involving a head injury? Then, I ask you, if you continue to not wear a helmet, who are you trying to fool? Certainly not the ER doctor.
John