[QUOTE=kdow;7812333]
They probably prevent SOME concussions. And with NFL players there is more going on - they sustain an awful lot of sub-concussion trauma on a regular basis that seems to contribute to CTE. So there is enough complexity there that I would hesitate to use it as a comparison. (If you are riding in a way to get lots of sub-concussion trauma, with or without a helmet, and you aren’t riding rough stock, I suggest some riding lessons. 
)
They are not magic force fields that protect you from everything, this is true. However, they do provide protection from a bunch of things and I have not seen compelling evidence that they cause or contribute to more issues than they prevent, so I personally am kind of baffled that anyone would choose not to wear one. (Similarly to a seat belt - in very specific circumstances a seat belt can actually cause injury or make a situation worse. But the vast majority of the time it improves your chances of escaping with no or minimal injuries, so we tell people to wear seat belts and ev have laws about it now.)
I really don’t understand people not making their kids wear helmets. I may vehemently disagree with you about your understanding of the risks such that you as an adult choose not to wear a helmet, but I don’t understand at all not making a kid wear one. The kid is not old enough to make the choice for him or herself (depending on age it may be something the kid can’t even understand properly to make the choice, due to brain development) and kids are notorious for doing stupid things and acting immortal (there’s that brain development stuff again) and the long term scenario for a kid who suffers a TBI who is not outright killed is pretty depressing - years and years of living with whatever problems the TBI causes?
(My opinion here is very colored by the fact that one of my housemates has all sorts of serious neurological problems as a result of a TBI from a car accident. I see how much it messes with her trying to lead a normal life - and she has recovered exceptionally well given how bad the initial injury was - and in terms of TBI survivors she’s probably “lucky” - she can perform daily care activities most of the time without help, she can’t drive but she can usually safely use public transit, etc. So she isn’t one of the TBI survivors who ends up stuck in a nursing home. But for all she CAN do, she still goes through a lot day to day, and there is plenty she can’t realistically do - like with the unpredictability of some of her less frequent but more severe problems, she would really struggle to live alone or hold down a normal 9-to-5 job that didn’t allow her to work from home at a moment’s notice. Plus she has issues like when she gets tired she has trouble communicating. It isn’t the worst thing I’ve known someone to live with, but it sure as heck isn’t any fun. If a helmet might help keep a kid from having to go through that? I’m sure as heck putting a helmet on said kid.) (Note that what I describe is after she is many years out from the injury. This is probably as good as it gets for her. Immediately after the injury, when she was ready for rehab, she had to do quite intense rehab. As I understand it she had to learn to speak again, and walk, and a number of other basic skills we take for granted.)[/QUOTE]
There is no question that brain injuries are horrible to deal with.
But we’re talking about helmets, and I can tell you that there is NO data showing that even those big football helmets prevent concussions. They prevent certain kinds of injuries - like skull fractures - but they don’t stop you from having concussions. You get a concussion because your brain is floating in fluid in your skull, like an egg yolk floats inside the shell. When you’re moving fast and suddenly stop, your brain gets slammed around in your skull. No protective gear worn on the head can prevent that.
