I’m probably writing this now because I had a helmet on when my bike flew out from under me on wet sand 8 years ago. I landed heavily on my left side, breaking a shoulder and cracking a couple ribs. In addition, I hit my head hard enough to blank out the last few seconds before I hit the dirt. My helmet was dented enough that the EMS crew decided to send me to a trauma center. Nothing wrong with my noggin, but better safe than sorry.
Bike helmets need not make you look like a teenage dork, either. My current one is a very subdued olive drab and could almost pass for something out of WW2.
Your link just reminded me of another reason I’ve heard for why people don’t wear helmets: anything that doesn’t have bits of plastic that dig into your skull is fairly pricey. I rely on my bike for transportation because I can’t afford a car (and if I could, I couldn’t afford gas/maintenance/insurance). Plonking down thirty bucks for something that I probably will never get anything out of is not desirable. I bought the cheapest helmet I could find, it still cost twenty bucks, and it’s uncomfortable to wear.
(Also, IMO, anything that increases the circumference of your head by ten inches is going to make you look like a total dork. Protective gear is very rarely anything but ugly and dweebifying.)
Bringing up Jaywalking is more of a ‘setting a good example’ then safety thing. While I agree that you’re not hugely likely to get hit if you’re careful Jaywalking, at the same time, what child just saw you do that? Same with wearing a helmut. I wear one, all adults (here) wear one, so kids are fine wearing them. If I Jaywalk and a kid watches me do it, they’re more likely to do it, and kids aren’t as careful as adults.
Don’t get me wrong, I used to Jaywalk ALL the time. But not any more. I don’t even run across when the hand is flashing anymore. I want to set a good example for whoever might be watching. Besides, I’m really not in THAT much of a hurry, are you?