Don't forget to mention that dooring isn't really problem in European cities. Most European cities separate the bike lane from parked cards. For people in bike lanes, that's the main risk that would cause an accident where a helmet would help prevent injury.
Same for San Francisco, NYC and pretty much every other city in the US. Only recently has SF begun to plan for the separation of parking and bike lanes. I believe a pretty significant number of bike deaths in NYC last year were attributable to dooring.
