I really can't believe people are arguing over whether or not one should wear a helmet while climbing....grow the fuk up. It is a personal choice; just as wearing one while riding a bicycle.
I recently was in an accident, hiking off a peak sans helmet....it probably would have prevented the head injury I obtained during the fall but who knows..maybe the helmet would've changed my mass of balance enough to where I hit the rock with my chin or face or "?"
The one problem with this world; everyone thinks they know what is best for the other person....Respect one's choice and if they choose to climb without a helmet so be it...