If a large vehicle hits you at a decent speed a bit of poly on your head isnt going to make any difference, your body will be broken...
It did to me. I was hit by a Toyota Starlet at a combined speed of 40mph (source: Police witness, I can't remember). I hit it head first, having flown over the bonnet. The police on the scene said I would be dead were it not for the helmet. I sustained a fractured skull, broken arm, broken other hand, broken shoulder, and broken nose/cheeks/teeth/jaw. Oh and a smashed helmet which found its way into a hospital bin. The car had a dented bonnet and a broken front screen, bits of which the A&E doc had to pick out of my scalp.
A few points in answer to others: "My instinctive reaction would save my head". I suspect my broken arms are the result of putting my arms out, this probably reduced the impact *a bit*. Did it save my head? Evidently not.
No helmet can protect against all possible accidents. If you have to land on your head though, then you are more likely to escape injury if you have some form of protection.
If you are going to hit a car on a bike then you will naturally go over the bars and fly head first, therefore there is a distict possibility that you will hit something this way.
I can't envisage an accident where a helmet would make things worse, or not easily at least. I can envisage plenty where itwould help.
I don't think my behaviour chanes significantly in a helmet. No "risk compensation" factors threfore apply, or are significant *to me*.
So, in terms of risk analysis *for me*, I don't think the use of a helmet makes things worse in any situations I can envisage. Sure it could "hook up" but this is unlikely. Sure the 300g weight could make it worse, but come on. 300g? Can I envisage a repeat of the accident? God forbid, but yes. I cycle in traffic and it was a classic violation of ROW collision. These cause the majority of motorbike accidents and fatalities AIUI. Since the accident I have had one near miss involving yet another blind car driver who pulled out of a side turning. Fortunately I saw it coming and by braking heavily I managed to stay off the bonnet and out of the screen. Had I not managed this then it would have been a carbon copy of the near-fatal accident.
So in short, if others want to wear helmet or not, be my guest. Either way it's your head, do as you wish. I will, for me the anti-helmet arguments hold about as much water as anti-seatbelt arguments. The fact that I have driven hundreds of thousands of miles without needing a seatbelt, and that in certain circumstances (eg slide off the road into deep water) you might be better off without, don't negate the advantages.
I suspect a number of people who don't want to wear a helmet want to justify their position, and I can sympathise with them not wanting to be moralised to by some pro-helmet crusade.
By the way, if anyone wants to open the Stevie Wonder School of Advanced Driving here in Leeds, I'm sure there would be plenty of takers. ;-)