I have smacked my helmet against the ground at least twice, with my head inside and had no injury. Can't say I regret having wearing a helmet. Also, I have a friend that spent 2 weeks in the hospital after passing out on a bike and slamming his head on a brick wall without a helmet. He has a scare that runs from the front of his ear to the back of his neck. My son and I rescued a bike rider who had a head injury one day. My son never complained again about wearing a helmet. Granted this evidence is anecdotal, but as we learn more about head injuries it's becoming apparent the importance of protecting it. Granted other activities are as bad or worse for getting a head injury. Personally, ice skating comes to mind, as well as most contact sports. that said laws that keep people from hurting themselves are probably better for those under 18. After 18, the government can put you in harms way so you probably should have the right to do the same.