So your saying that having a protective layer on your head is less safe than not having one.
###In a whole population, yes.
Bear in mind I am talking about mandatory helmets for ALL. Not voluntary helmets.
I can guarantee that if someone was about to drop a brick on your head and offered you the choice of wearing a helmet, you along with any right-thinking person would take that helmet.
###But if it was a feather cushion would they? And do you wear one when walking? Cos they help too.
A cycle helmet is designed to absorb a certain amount of energy. This means they have a sweet spot in which these work. They will not work when the energy is too high, low or when you break your neck *to put it bluntly*
For a very low speed fall: A helmet won't hurt, but won't help either as injuries are minimal anyway.
For falls at a certain speed: A helmet will reduce injury and is recommended, see for example cycle racing, downhilling.
For falls at a very high speed: A helmet may not help anymore as the impact energy is so high that the amount absorbed by the helmet makes no difference.
Note how the speed makes a difference. If a helmet invites you to riskier behavior OVER what it can absorb there is no benefit.
Now the next big thing: Crashes with cars.
That is where it gets problematic.
As stated above the impact energy the helmet can absorb is quite low, and only on the head. If a car/bus/truck crushes you, there's no help If you don't hit your head, it's no help either.
So the window where the helmet *may* help is if you hit your head in such a manner that the impact energy is not too high. This is where the jury is out.
Now looking at the above examples you would think "ok, helps against pot holes generally, might not work against cars, so surely there will be some benefit in mandatory helmet laws?".
The data doesn't support this. Now, there can be many reasons.
For example: Car drivers may take more risks. Cyclists may take more risks. The reducing in cyclists may mean more risks. There is however some countries where cyclists reported MORE injuries per mile cycled. Which is exactly what you don't want, you want the helmet to keep you safe.
The reason you dont think helmets are necessary is that you dont think you will ever have an accident. No matter how safely you ride, you cannot reduce the chances of having an accident to zero.
###I agree that you can't reduce the odds of an accident to zero. However, in the style of cycle I do (commuting in town) the main risk is a car collision. There's no proof a helmet is going to do much at all there, there is some proof cars give helmet wearing cyclists less room, which increases the odds of an accident.
Would I do downhilling/road racing/snow cycling/cycling on really bad roads yes I'd wear a helmet as then the benefit is clear.
The internet is a big place, so is The Netherlands where accident/injury rates are much lower than the UK...and so is helmet wearing. In Australia accident rates also went UP after a mandatory helmet law.
Therein lies the snag.