For the sake of this discussion, I don't care about what people eat, what pedestrians, car drivers or passengers wear, what you wear when you jump off the house, or any such things. Most bike crashes are simple affairs: clip-out failure, scraping a curb and falling, hitting a pothole, or maybe a bump from a car. In each you will fall with varying degrees of force from the bike, and there is a good chance of hitting your head. I would much prefer hitting my head with a bike helmet on, than not. I would prefer not having the accident in the first place, but as Lance said, if you're afraid of falling off the bike, don't get on it. For the more serious and less likely accident - getting hit by a car at speed, etc. - a helmet won't help, nor will anything else other than avoiding the crash.
There is a good chance, when riding a few thousand miles a year on the road, that at some point I will have a significant crash that will bounce my head off the ground. Maybe the helmet will save me from a knot, maybe from a fracture, maybe from a subdural hematoma, or maybe from nothing at all. I am not convinced that drivers behave less safely around me because I have a helmet, and I do not believe that I take more risks because I have a helmet. It's also possible that a helmet could cause one kind of injury while preventing a different one (Seatbelts help preserve your face, chest and head at the expense of your neck and back - I'll take whiplash over smashing into the windshield any day.) Those things are possible, but unlikely. So as I said in a previous post, the cost of wearing it is minimal, while the benefits are significant.