I'm a member of the "Saved By The Bell" club. Bell Helmets sends membership certificates to those who crashed and hit their head hard enough to damage or destroy one of their helmets. I fell on a slick road at a slow walking speed when the bike went sideways out from under me and I hit my shoulder hard enough to break a bone and hit my head hard enough to crack the helmet in three places. I had a mild concussion but it would have been far, far worse without the helmet. You don't have to be going fast to get hurt. I never rode without a helmet prior to the accident and certainly not after.
All the above being said, I'm against helmet laws. People have the right to take chances and, if they refuse to use reasonable safety equipment, it's their choice. What I don't like is those who get hurt blaming (and suing) others for what they did to themselves.