Unironically the biggest flame-wars I ever saw on forums back in the day was on whether or not mandatory bike helmets made cycling safer or more dangerous.
I can understand, I’ve had some awful bicycle accidents while not wearing a helmet and the helmet would have made no difference. My knees, hands and elbows have been through a lot but I have never hit my head. Even while skateboarding the one time I hit my head a helmet would not have helped. In hindsight I should have worn knee pads a lot more often but then I wouldn’t be able to tell if it’s gonna rain or not from the feeling in one of my knees :)
However if I had to ride on a public road with cars zooming pass me recklessly I would absolutely wear a helmet on a bicycle.
And there are countries where everyone rides a bike, and they are not usually the ones with mandatory helmets. When you hit someone with a bike you are less likely to kill them than when you hit them with a car, so more bike riding means less deaths, without even considering the effects of air pollution.
Helmets are fine for sport riding, but inconvenient if you want to ride 5 minutes to the shops on a whim. And that kind of riding is usually less intense and safer, I presume, anyway. Football has helmets, walking doesn't.
Those countries also have a higher number of brain injury cases vs countries where people wear helmets.
If you are hit by a car a helmet will do approximately nothing. However there are a lot of accidents that happen where you are not hit by a car where a helmet will help. (and even more when knee and elbow pads are what you need)
A helmet can make a big difference in saving your brain if you are hit by a bike. Or if you hit a slippery spot and fall off your bike. Or - hundreds of other things that happen.
cars are too big and heavy for a helmet to make a difference - but they are not all that can go wrong. Even in car heavy US there is more than a car that can harm you.
Can't resist taking this bait, but I feel like the consensus is pretty much that as an individual, choosing to wear a helmet will make you safer, and as a society, mandating bike helmets (and other measures that will cause people to use transportation methods that are more dangerous to others) will make everyone less safe.
Of course, it's hard to prove. But I think you'll generally find that, if you compare the number of injuries/deaths while cycling in countries with mandatory helmets per km will be higher than it is in the Netherlands, where they are not mandatory.
Comparing the Netherlands with some of the best, if not the best bike infrastructure to other countries without said infrastructure seems very reductionist. To get anywhere near an interesting number you would have to compare the number of injuries to the total number of accidents including cyclists in countries with comparable bike infrastructure and differing helmet policies.
Yeah that's why it's hard to prove. However, it does show that infrastructure experts who actually care about safety (and have achieved the safety numbers to support it) reach for a lot of other measures before they do helmet mandates.
However if I had to ride on a public road with cars zooming pass me recklessly I would absolutely wear a helmet on a bicycle.