how many rafters do you know that have died of head injury? most deaths are flush drowning, entrapments, or heart failure I can't think of one I know that died of head injury. that said... I always wear a helmet on class IV or higher and recommend everyone do so as well.

darwin award is more like not wearing your pfd. helmets are a great idea but hardly absolutely necessary. last year I was at the put-in for the grand canyon and realized the one thing I forgot was my helmet (I like to wear it on the big class IVs). well did I turn around and go home? no I went without the helmet just like most other grand rafters.