And for the record, our son willingly chooses to wear his bike helmet, without supervision. Without coercion, without threats, without intimidation, without punishments, without "logical" or imposed consequences.....
And I, personally had a huge bike accident, sans helmet at age 12 and "I turned out just fine".
(flipped the bike, using the front brake only while speeding out of control on a West Virginia hill/mountain road, head landed on gravel, yada, yada. Stiches in my head after riding to the ER in the Ambulance, the works.)
And I have a friend whose husband, avid commuting bike rider, with helmet
was left severely brain damaged after being hit by a truck.
No guarantees, but IMO an adversarial parental relationship is more damaging and more dangerous than most children's probable head injuries from bike riding. From the looks of the surrounding neighborhoods, bike helmets are more negotiable than tooth brushing appears to be.
Pick your battles, if you want to battle. But I trust my role as an advocate, not the role of adversary.