Oh this makes me sad. I went on a group ride last week where, once again, I got unsolicited comments about the fact that I wasn't wearing a helmet. One young woman actually listened to what I said in reply, rather than getting annoyed, and eventually said, 'Do you know, I'd never even considered that I could ride without a helmet. I just assumed it was what you did.' (It transpired that she was a scientist so used to evaluating evidence, hence the patient listening I think.) It's becoming part of the uniform, which is not necessarily to cycling's advantage.