I wear a helmet. My wife does not.
One should educate themselves, then make a personal decision.
Agreed. But all too often I see the libertarians around me making a personal decision
as if they are the only one in the room. I won't venture whether you and your wife have had that discussion.
The reasons one wears a helmet are the same reasons one buys life insurance. It's not because it is
likely you will get hurt, it's what happens on the
off chance your skull does come in contact with the pavement. "I've never hit my head riding a bike" is akin to "I haven't died so life insurance is a waste of money". Past performance is not a guarantee of future returns.
Every doctor I've ever been to has pretty adamantly insisted on my kids or myself wearing a helmet. IMO they are the subject matter experts when it comes to injury, and when people choose to ignore the subject matter experts, well, I'll just leave it at that. When they, and not some cycling enthusiast, start telling me helmets are overblown I'll gladly listen to that argument and gladly ditch the helmet. Until then...
As far as the argument about running (or walking) helmets go, I think people are forgetting the laws of physics. If you wipe out at 15, 20, 25 MPH the potential for harm is much greater than at 9 MPH (just better than a 7 minute mile running pace). Force equals mass times velocity. If you are tooling along at a nice 18 MPH clip your head will hit the ground with a force several times that of a fall while walking at 3 MPH. So that is why walking helmets are unnecessary while riding helmets are. The human body did not evolve with 18 MPH collisions as part of the mix.