I abolutely refuse to wear a helmet while on a bicycle. And, really, unless you are in a big race or riding in heavy automobile traffic, do most people need a helmet while riding a bicycle?
abolutely = absolutely
I do, but I guess it depends on where you ride, how often, and how aggressive you are when you do ride. Just like there are runners, and then there are joggers, there are serious athletes that ride, and there are posers.
I like to think I'm a serious athlete when I ride - both mountain biking and road biking. A couple of hours riding in the woods up and down steeps, with assorted roots, rocks, turns, mud, and trees (that don't get out of your way!) - that's a real workout! Or riding 45-60 miles at an 18-19 MPH pace on a road-bike, that's a real workout too!
I've actually broken a mountain bike helmet when I took a spill and quickly found the ground - my head (helmet) hitting a rather large rock. Probably would have been badly concussed (or worse) if I'd dared to ride without. When you're going fast, and things go wrong - they go wrong quickly, and you don't have time to react.
So yeah, a helmet is actually a wise thing.
Of course not. You need a helmet when you're bouncing your head off the road, or a rock, or another bike.