What ever doesn't kill you only makes you stronger. My dad rode dirt bikes without a helmet one countless occations back in the 70's and the only scar he has from a helmet related crash (which was on a bike) was a goose egg up on the old noggin. Which is still visable today.(the lack of some hair doesn't cover anything up.
Ohhh man I hope my dad doesn't monitor me on this site. If so, I'll be gettin' a beatin' in the next few days.