Wow, quite a thread here. I didn't read it all, way too long, but I scanned quite a bit. Its very familiar and very much like all the various (and numerous) helmet threads in the motorcycle world. Its always amazed me how helmet use can be such a hot polarizing subject.
So, a quick disclosure of my views. Bicycling, I wear one sometimes. Motorcycling, I wear it all the time. I don't really care if someone else does or not. I have and will fight helmet laws whether it pertains to bicycles, motorcycles, skateboards, cars, or walking down the street. I believe in a persons right to make decisions for themselves good or bad. The ability to make those decisions is I think a basic right. Its my life, your life, enjoy it as you wish. When the government can tell us we have to wear a helmet, its not long before they can tell us we cant take risks at all and bicycles, motorcycles, mountain climbing, scuba, whatever, it all can be gone.
So OK, all that said, I have a bit of experience with TBI's. I've had in my enjoyable, adrenaline fueled 57 years, at least 5 concussions. That's 5 times I've been knocked well and truly out. How many actual concussions I've had I don't know but I used to play ice hockey and on more than one occasion got put into the boards hard enough to come off dazed and a little wobbly on my blades. Were they concussive? Maybe, probably, perhaps, I don't know.
My first concussion was on my bicycle at around 7 years of age (riding the bike in my avatar). Out long enough that my friends carried me home before I woke up. My second was ice skating a few years later. My last was just this last March in a stupid work accident, which was also the only time when I wasn't engaged in some risky but way too much fun form of entertainment. I fell, I don't know why as I don't remember and nobody saw it, but I fell. Unfortunately I was standing on the back of a pickup truck and seem to have taken a swan dive to the ground. I'm still not able to return to work. I am however able to ride my bicycle again, and drive a little, but I don't feel well enough to get back on my motorcycles yet. Sucks being hurt. What really sucks are the memory problems and the problems with concentration and comprehension, and a serious issue with details. Problems performing tasks involving detailed processes. Typing this for instance is taking me forever and I had to try three times to get a stupid rear brake cable properly run on one of my road bikes the other day (I've been building bikes since I was in Jr. High School). I repair old cameras for fun, but since last March I pretty much just break old cameras so I've put them away till a later date. My neuropsychologist says she still thinks I'll get better. I hope shes right.
So I guess you makes your choice and takes your risks and enjoy your life as you wish. Just don't ignore the possible consequences. Oh, and don't tell me helmets don't work. To some extent at least. Bicycle helmets are minimal. Too bad they cant be as big and effective as motorcycle and auto racing lids. Those things have saved my life at least once, perhaps twice. Even as a minimal thing though they will at least keep you from scrapping your hair off, which will hurt and probably ruin your day. So why don't I wear one all the time? Hell if I know, I'm just human I guess...