I'm not exactly Lance Armstrong, so I can barely make it to 25km/h on my bicycle (without a good tailwind or a downhill run) and I certainly can't maintain it for long.
What's the bottom end of that effectiveness curve look like?
It's 100% clear that helmets have zero effectiveness at 0km/h[1] - I bet the "effectiveness" of helmets is statistically the same a zero at 1km/h and 3km/h as well - where's the data that shows the shape of that curve? How does that compare with various categories of cycling?
I note that what the linked study/article "proves" is that if you have a crash in which you might die, a helmet will improve your outcome in some of those cases. To me that has (at least) two obvious responses: 1) wear a helmet, or 2) don't have those sorts of crashes. Me pedalling to the shops or the cafe at 10-15km/h on cycle paths or quiet backstreets is enormously safer than me riding at 25km/h on a busy or main road, or on a downhill mountain bike course - with or without a helmet. Why to "the helmet guys" get to choose which risk minimisation strategy I'm required to employ?
[1] to be more accurate, the benefits of having a helmet on while stationary on a bicycle are no different from the benefits of having a helmet on while standing still - something the safety-crats haven't (yet) suggested is necessary...)