I don't know how many such collisions you've been in, but I've been in about 6 motorbike accidents of fairly light severity, including hitting a car at about 50km/h. I bounced off the front of that car and landed head-first on the road. But I had no injuries at all - in large part because I was wearing a helmet.
That said, I'm not in favour of making bicycle helmets mandatory, and I think cyclists should be allowed to use the pavement for safety, as long as they are courteous and don't go too fast (no more than 10km/h or so) when close to pedestrians.
Another thing you'll rarely hear bicycle advocates say is that cycling on the pavement is safer. It most definitely is not, due to the speed difference between pedestrians and cyclists. This is not only dangerous to pedestrians: drivers aren't used to checking for fast moving objects on the pavement. Worse, pavements are rarely constructed with good vehicle visibility in mind. It's also hard to figure out which rules apply (pedestrian or road?), unlike when everyone is sharing the lane.
And motorbike helmets are actually very similar to cycle helmets under the shell. Biggest differences are abrasion resistance from the shell and more coverage on average, but 1/2 helmets - brain buckets - are very very similar. Indeed I see a certain percentage of London cyclists wearing helmets that would be legal on motorbikes in US states with mandatory laws.
German consumer organization tests showed that lots (60% or so) of the helmets for sale in Germany didn't even meet the head-on-collision tests as the testing isn't done by an official institute...
Wearing a cycling helmet makes sense when you've got a good chance of hitting something straight on. Like mountainbiking and hitting a tree or speed cycling at 50km/h, bend over your handlebars.
Kids? Regular cyclists? Mum with groceries? No way. Or at least: other things are more effective. Like wearing a cycling helmet as a pedestrian (who apparently hit things with their head more often!).
Though it's hardly a new development. Seat belts have been mandatory for decades. People complain about safety restrictions like these at first but seat belt laws have been around long enough to reduce the complaints to a mere mumble. So may it happen with helmet laws.
I think there's too little data about road accidents publicly available. I think all documentation from police investigations of road accidents should be anonymized and made public after some time.
The main reason being given is seat belts for drivers and helmets for moped users. Info in Dutch from the official statistics bureau: http://www.cbs.nl/nl-NL/menu/themas/gezondheid-welzijn/publi...
Any policy which reduces the number of people who would otherwise choose to bicycle is de facto worse for people's health. If mandatory helmet laws decreases the number of bike trips by even one, it's a net loss.
I use a bicycle to commute to work every day. I think, I really should get a helmet. But I do not think they should be mandatory. I have been run over (more like bumped into) by a car more than once. But I was lucky and had no injuries at all. With my motorcycle it is a whole different story I had two real accidents and thanks to my helmet I am still able to write this.
I do not look the news for that kind of things but I have never heard of any cyclists getting killed in Japan at least in the recent past.
Helmets are stupid because the biggest problem is to avoid car and cyclists collision in the first place. Having something on your head will never save you if you get into a collision at 50km/h.