Thanks, Dan. Oil on troubled waters, everyone take a deep breath, now exhale, and think nice thoughts about our fellow cyclists. I find the intensity of feeling about helmet-wearing hard to fathom, but that's probably my problem. No matter.
To me, it's simply a question of risk management. I'll be delighted when Ontario/Ottawa makes a serious investment in cycling infrastructure, and will applaud when car/SUV/etc drivers do not regularly (that is, daily) try to kill me when I'm on one of my two-wheelers -- but I doubt I'll live to see either of these happy conditions. In the meantime, wot to do--particularly, what can I control?--to limit risk while I ride my beloved 2-wheelers? There's the usual counsel--stay off arterial roads, use a mirror, learn to anticipate dodgy situations, assume that car drivers (especially young guys in high-end German cars) really are out to get you and/or do not see you and/or do not care about what they hit/brush/etc., wear hi-viz gear just in case they are looking for cyclists. Me, I add "wear a helmet" to this list. (I also wear a skullcap under mine, being follicly challenged and having Scots/irish/RodLaveresque colouring.) The reason I do is hard experience: nearly 50 years ago, I came off my motorcycle at low speed, maybe 25-30 kmh, when my front wheel slid out as I dodged a kid on a bike on a gravel country road. I did a three-point landing over the bars, head-shoulder-elbow, sorta-tucked-roll. I wasn't badly hurt, just a bit of skin off my bare elbow (how dumb can you be??) but my helmet was a writeoff, with a deep gouge just above my temple. I was glad at the time, and since, 'cos I've been mostly happy in my life and I think my family (all post-helmeted-spill) share my retrospective view of that day.
My daughter, returning to Canada and resettling in Toronto after five years in Berlin, surrounded by Real Cycling Infrastructure and an advanced cycling culture, now faces the helmet question. With a low-key nudge/plea from me, she's decided to wear one: she doesn't like it, and she knows that it won't help her if a GMC Suburban clouts her at an intersection, but it does offer a measure of protection to her head if she comes off her bike in an urban setting which lacks the supports of Berlin's cycling ecology. I said to her, "Why even take the risk?" and she had already figured it out. (She's usually a step or two ahead of her dad on most matters...)