I wear a helmet (with a torch on so that, should I mistime a handlebar somersault, I risk ending up with highly illuminated grey matter) but I'd campaign against it and support non-helmeteers.
Safety is not just about protecting yourself, it's equally about not putting others in danger. This gets routinely forgotten by motorised road users and car manufacturers who think primarily about self-protection and neglect the protection of others. If cyclists are to be forced to wear an inch or so of polystyrene around part of their heads, cars should be forced to also be wrapped in polystyrene foam to protect others from the dangers they pose. Any increased safety would be extremely minimal, of course, but, then again, helmets don't provide anything more than minimal protection either.