There is a helmet section in the Campaigning message board, but it’s ‘interesting’ to say the least…
I don’t think anyone is advocating not wearing a helmet, i.e. trying to persuade others not to wear them, but some choose not to do so for a number of reasons. If a helmet was undetectable while wearing it, didn’t have to be carried around, didn’t mess up hair or trap sweat, didn’t get bugs stuck in it, and had proven protection/injury reduction in likely biking scenarios, then I’d imagine almost everyone would wear it. But it doesn’t exist. After a websearch, the only helmet I got enthusiastic about buying was a concept/competition winner, and not actually on the market. I’m still looking though.
In the image above, the helmet has doubled the size of the woman’s head, making it a larger target for impact. It sits too high on her head, is likely to slip on impact from most directions, which leaves her with a tourniquet around her neck and a large lump of plastic likely to get stuck/dragged along.