I hate my helmet, it itches and it's uncomfortable, but I never ride without it, I just feel naked.
Is it my business if other people wear one, well under 18's IMHO it should be mandatory to wear a helmet at all times while mounted, no exceptions.
As to other adults, well I can see in the USA we can argue free choice and each to their own, but in the UK and Canada?? Well I've lived in both countries with their wonderful medical systems, and yes I think it is somewhat my business, if I'm paying into a central fund for health care I would prefer it if you at least tried to stay out of hospital, and wearing a helmet can prevent serious injury.
BUT, I'm not a helmet fanatic by any means
Unless you are a minor