[fsloth]

In what way does the need to wear a helmet reduce your capability of cycling? Last time I checked helmets were sold in the same shops as bikes.

[tempestn]

Slight inconveniences most likely. If you commute by bike, you then need to carry the helmet around with you or risk it being stolen. You have helmet hair, which sounds trivial, but might be an issue for some people riding to work and such. Things like that. Nothing huge that I can think of, but I'm sure these things discourage cycling to some extent, for some people.

[freiheit]

Forget the theories and look at the data. When governments (such as Australia) have passed laws making helmet use mandatory, bicycling rates have gone down.

[boyaka]

The fact that they require money, maintenance, and effort to use? It may be minimal but it is there.

[welly]

What maintenance does a bike helmet need?