Over here, the reasoning against helmets is not that they make cycling look dangerous or prevent people from riding a bike (maybe because there actually are a lot of people cycling), but that the risk of being injured while riding a bike without a helmet is lower than the risk of a head-injury while driving a car or walking - still nobody would wear a helmet doing this.
I don't know if this argument comes from twisting the outcomes of some statistics, or if it actually makes sense.
What seems clear to me is that while this may be true, still, if you happen to fall on your head, it's better to wear a helmet while doing so - even if the car driver that runs you over doesn't (guess that's the difference between statistics and reality).

I myself am not sure what to think. Wearing a helmet while biking was unusual when I learned to ride a bike. Until I was grown up, it was never heard of that you could even consider wearing a helmet while cycling. Today, it's still not very common to wear a helmet when riding a bike for errands or into the city (except for kids). But nearly everybody uses them for doing cycling as a sport.
In the last years, helmets (and other protective gear) were heavily promoted for skiing, another sport that wasn't considered dangerous when I grew up.
I am not sure how much of the discussion about protection is just marketing new expensive equipment.

I fell on my head twice. Once while riding my bike on ice (while wearing a helmet) and once while helping my mum in the garden and falling from a stair onto concrete (while not wearing a helmet - 2 weeks in hospital in the midst of summer!). I guess if had been wearing a helmet I wouldn't have hurt myself as bad - but I'm not sure if that means that everybody should wear a helmet while being in the garden

My husband and I are still considering buying helmets for the city. Just in case.