I grew up before the era of helmets.  I remember well, riding without one, and understand Key's enjoyment of the breeze.
 
However, I have ridden with helmets since around 1995.  I will not ride now without one, even on the trike.  Why?  One reason is I want to set a good example for my kids to wear their helmets always.  Another reason is when I crashed last October on my Giro, as the side of my head smacked the hard packed ground on Stacy Ave, I clearly remember thinking "That should've hurt a lot more than it did!".  My helmet broke.  My head did not.  Third, the helmet I have not only holds a helmet light on it, and more reflective tape, it also is a lovely Toxic YellowGreen color...all the better to see me with, my dear!
 
Do we really need a law mandating helmets (including motorcycles)?  That's a grey area, but keep in mind that all of us are in some way, paying for the support and care of those non-helmeted folks who are permanently TBI'd.  (we pay via increased insurance costs, increased taxes for the medical support of the uninsured, etc).  It ought to be a choice responsible adults can make, and I for one, choose to wear my helmet.