I am really not sure how helmets prevent head damage. I have been crashed into by cars on a few occasions, one time bouncing off the hood/bonnet then spinning through the air but I didn't bang my head because I put my hands down to break my fall. I have also slipped on oil patches on a few occasions while cornering at high speed but again I never hurt my head because I put my arms down to break my fall. On one occasion I hit a deep pothole and somehow went flying over the handlebars, my whole bike up-ended on the front wheel and I went completely over with my bike following me but again I put my hands down to break my fall, I rolled thereby making sure my head didn't hit the floor. I can easily use my neck to angle my head away from the floor, which in combination with intelligent usage of my arms I can avoid banging my head. I am not a stunt-person, I am strong but not noticeably so, I don't think I am unusual regarding my ability to make sure my head doesn't hit the ground, I think I am merely intelligent and fit. Unfit stupid people should be forced to wear helmets perhaps.
Statistically I think elderly people are more likely to suffer traumatic brain injury when merely walking down the streets, but should elderly people be forced to wear helmets while going about their everyday affairs? Drinking alcohol also significantly increases the risk of falling (not while on a bicycle), drinkers are more likely to suffer head injuries, thus maybe all people drinking alcohol should be forced to wear a helmet?
There is a tendency amongst some people to hysterically clamour of strict regulation regarding every aspect of our lives, for safety, which is an oppressive type of control. Obesity kills far more people than cycling thus maybe it should be illegal to eat more than a certain amount of calories each day, maybe government sensors should be compulsory to monitor what people eat? I think the sane solution is to allow people to do whatever they want providing they are not hurting other people, thus elderly people should not be forced to wear helmets when going about their daily affairs, cyclists should not be forced to wear helmets, and governments should not control what we eat to prevent obesity.
So Preston Sturges you think wearing a helmet would prevent forehead scars but I am not sure how valid your viewpoint is. I think if a cyclist is hitting the ground face first then the forehead part of the helmet may ensure the cyclist receives a massive nose, teeth, or chin injury. I would prefer to scar my forehead than have my front teeth smashed out, or are you recommending full-face helmets?
From my viewpoint I think wearing a helmet would actually be more dangerous because the increased head-size due to the helmet could possibly restrict my ability to move my arms quickly around my head area when I agilely roll to break my fall, thus wearing a helmet could cause a serious head injury for me if I crash because the helmet would likely restrict my movement, my agility, I would be less free to move in an unrestrained manner, thus my ability to self-protect my head could be diminished due to the physical restrictions of the helmet.
I think freedom should triumph over safely especially when freedom hurts nobody else. Via excessive regulation for safety we risk creating an Orwellian open prison. Reliance on externally imposed safety means people are less inclined to depend on their internal controls, their brains, which means people actually become more dangerous because they are ceasing to think, their thinking, independence of mind, has been supplanted by external control thus their self-reliance and self-determination withers, they become institutionalised robots who need to be guided and supervised in every aspect of their lives, they cannot think or act for themselves, they need to be told what to do all the time, they cannot think how to protect themselves they need an authoritarian protector.
There are my reason why I think helmets could limit physical and psychological reactions to danger.
I think the real reason some people clamour for cyclists to wear helmets is that they resent the independence of mind enjoyed by cyclists. Generally I think the clamouring comes from motorists who want to punish cyclists because motorists hate the freedom cyclist have, thus the need to protect health is a specious argument because the actual motive for the clamouring is punitive.