Honestly, I don't understand the reasoning for not wearing a helmet. I wouldn't mind at all if I was riding in "work" clothes or dress clothes and had my helmet on. It's a piece of safety equipment, and like GLC says, we need to get people to think it's "cool."
I know people don't wear helmets in other countries, but truthfully, when I rode a cruiser on the beach in Hilton Head a few years ago, DH had to convince me not to wear my helmet. We had brought them to go mountain biking. I didn't wear it, but I was worried the whole time I was going to crash and land on my head. I don't care if I was going 5 mph on sand; it's just that ingrained. Or maybe it's my Jewish mother neuroticism.