I'm surprised that people can seriously doubt that helmets afford protection. I can accept that people may prefer not to use them, but to me, when your hurtling down a hill at 50 miles an hour on a bike, it's pretty obvious that if you hit something, there's a fair chance you'll be propelled head first. Again, I may be wrong, but if I'm going to hit something hard with my head, I'd rather have protection. I can't quote sources to state that it's less harmful to whack your head on tarmac wearing a helmet than without, but I'm willing to participate in trials, so long as I'm the one wearing the helmet, in fact, I'll place a substantial wager with the chap without helmet, than my head will hurt less than his.
I fell down a hill many years ago, hit some rocks with my head, had around 50 stitches, maybe this makes me soft in the head, but to me, whilst I totally support personal choice when it comes to helmet use (and I'll not bother if I'm pootling around, I would not be without one when riding fast. Just my two penn'orth though.