All too many of those who chose to wear helmets look down on those of us who don't, as ignorant neanderthals. (Many of) the helmeted simply cannot accept that it's possible to make a reasoned decision that's different that theirs.
I don't know how often you hear "what's that on your head?" or Yo! planning to fall?" or whatever, but non helmet wearers are constantly assaulted by "where's your helmet?" from sanctimonious helmet wearers. Nowadays I hear it from non cyclists as well. Mothers yell at me because I'm a bad example for their children, and motorists feel free to add to the chorus, as they pass.
Feel free to "educate" newbies about helmets, but when you see someone riding in control, who looks like maybe he's experienced, figure that by now he's heard it all. If he chooses to forgo a helmet it's a reasoned decision, so stifle the urge to proselytize.