It started on Twitter, where a conversation caused me to have a realization that's obvious in retrospect:

@cwage: so, B-cycle is awesome, but it occurred to me recently that it basically promotes people riding bikes in the city without a helmet. discuss.
[...]
@cwage: let me rephrase my earlier tweet: Nashville is not (yet) a bike friendly city. not enough infrastructure. not nearly enough bicyclist density
@cwage: thus, automobiles lack awareness, and B-cycle users are largely inexperienced riders. the combination (without helmets) is terrifying

@cks: @cwage I think the combination would still be terrifying even if the B-cycle riders wore helmets.
@cks: .@cwage Wearing a bike helmet is not a substitute for avoiding getting hit or crashing. It's just a minor safety boost if you do.

There is a lot of fuss made about people being irresponsible when they don't wear bike helmets and about how you need to wear a bike helmet to be really safe and so on. Some places have mandatory helmet laws, some places just strongly encourage it through social mechanisms (Toronto is the latter). Helmets may or may not increase your safety in practice for various reasons; there are serious arguments that they don't help once you take a total view (instead of focusing just on what happens once a cyclist gets hit).

But all of that misses the issue that I summarized in my last tweet: helmets are only a marginal improvement and if they do any good you're already in trouble. They're a consolation prize if you have an accident; you may be hurt but sometimes you'll be hurt less than if you hadn't been wearing a helmet. It's much more important not to have the accident in the first place. Getting people to wear helmets is something you think about after you've tried to keep them out of accidents in the first place. Someone who is wearing a helmet but riding unsafely or in a dangerous situation is much worse off than someone without a helmet who is riding in safety.

(This is especially bad if wearing a helmet has convinced the cyclist that they can ride more aggressively and less safely because now they have protection. Wrong (but very human).)

That's what I mean by helmets being a distraction. In practice the 'wear your helmet' advocacy has wound up causing people to focus on helmet wearing to the sad exclusion of keeping cyclists out accidents. Given limited resources, limited attention spans, and human psychology, we'd be much better off if people ignored helmets and focused on accident prevention.

(I understand the various reasons why people can't, including that it's very hard to pass up an obvious harm mitigation measure.)