Helmet or no helmet, I think as long as it's not required by any laws applicable to the jurisdiction of the area being ridden in, then it's a personal decision. I'm sure I could find things unsafe about the riding habits of any that say a helmet is a must. Many of those habits worse statistically for injury and death than not wearing a helmet.

I myself will always wear my helmet for cycling. Just like I always where a seat belt and shoulder strap for driving. But since head trauma, even for belted persons in a car is now the number one killer of passengers and drivers in auto accidents, why are you people not wearing helmets in your car?