I received a concussion and 5 staples in the back of my head from a crash where I wasn't wearing a helmet. I'm not officially qualified to evaluate my injury and accident, but I can't logically see how I would have been hurt nearly as bad if I had been wearing a helmet.
I think a lot of the arguments against wearing helmets are like the arguments against seatbelts. there are incidents where a helmet or seatbelt can actually cause injury, but for 99% of crashes, it's beter to wear one.
wearing a helmet is the new rockin a tri-spoke.