I believe helmet wearing should be a matter of personal choice, and am totally against any kind of legal compulsion.
More anecdata:
I started wearing a helmet about 25 years ago, but only in town. I've always understood that helmets could provide some protection against low-speed falls, but reckoned they wouldn't help much if a car hit me at 60mph+ on a country road. During those 25 years I came off a few times, on ice, oil, and once when a taxi came out of a side street without stopping. I picked up some bruises but never hit my head. Meanwhile, one friend was killed, and another one and a cousin suffered serious head injuries falling down stairs at home.
Last year we had an unusually hot summer here, so I stopped wearing the helmet. I noticed that cars gave me more room and generally drove more considerately around me! Maybe it helps that I am a grey-haired 60-something -- a real person, who might be somebody's much-loved granny/mother/wife....
Don't forget the element of risk compensation, both on the part of motorists ('I don't need to pull out/slow down as s/he's wearing a helmet') and cyclists. From a book of hill climbs:
"....a helmet won't diminish the thrills of hillclimbing and it may even help you focus less on the danger of descending. Protect that precious cargo with a well-fitted helmet!"
[McKendrick, Hillclimbs on Scottish Lowland Roads]
I remember a poster on another forum saying that he regularly got up to 55mph on descents, but wouldn't dare do that without a helmet
! The same poster had earlier praised his helmet for saving him from serious injury -- he had been riding on a gusty day, sitting up no hands eating a sandwich, when a side wind blew him over.....
Some people are more prone to falling awkwardly than others - my brother-in-law fractured his skull just falling over his own feet as a teenager. As I said at the beginning, it should be a matter of personal choice and governed by personal circumstances. Just remember that a helmet is not a magic hat, and cycle shops have a vested interest in making sales.
I don't mind if other people want to wear a helmet but personally I feel safer without one.