Thank you to both Kate and Suzanne for not pestering me before now. I am doing my research and you're right--while not the most common injury, head injuries are the most likely cause of death.
And--while I agree with Kathy's comment about not caring since I'd be dead--I also agree with her and Kate's sentiment about not wanting those I care about to have to wipe drool off my chin. (AND sooo glad to hear from Kathy, by the way. Glad Bert is okay and you are both still riding!)
Imel, I may never convince Steve to wear a helmet, but I found a reference that likens riding risk to motorcycle riding--and he always wore a motorcycle helmet even before it was the law.
I do accept the risk of riding, and have the battle scars to prove it. I have two mounted injuries (arm and butt) and one unmounted injury (ribs). It's likely not an if but a when that I bounce my noggin on something. My noggin has to keep functioning for a lot of years--I can't retire for another 27 years--so risking mush-brain is risking a lot.
My friend Sasha--who has very personal experience with someone with a TBI--reminded me that even a full recovery may not lead to it being the same person they were before the injury.
Your arguments are all very compelling and I truly, truly appreciate the feedback. It won't stop me from being irritated at the helmet-police on Facebook, but for my own personal thought-processes, this has been invaluable.