I think that helmets are prudent protection for any activity that has a significant likelihood of head impact, and certain protection when one does in fact hit one's head. I am not sure that the likelihood is more significant for cycling vs. walking, climbing ladders, swimming, or even bowling, though. Risk perception varies widely from reality and to label all cyclists as having equivalent risk for head injury is not reasonable. I do wear a helmet when cycling and was glad that I did when a golf ball hit my noggin. Should the pedestrians on that road also wear helmets? Probably not, but do I think the golfers should consider wearing athletic cups.