Good points. What does your job have to do with riding helmets though? I'm the safety officer for our region where I work as a biologist and I still think it's a personal choice. At work you are required to follow certain rules to do your job. Outside of work, the decision still remains up to the individual and thankfully so.
Good discussion. I think it's an important decision for each and every person to make, on their own.
I'm still not sure what magical answer you are looking for as to why people don't wear them. I know that some people they cause migraines, no matter how many different ones they try. I know for others, despite the new advances in the helmet making, they make their head too hot.
Somehow, I don't think any reason would really be adequate for you though!
There is nothing in the world that can't be argued against. So my thoughts are to leave it to the people themselves to decide what they want to do as each person's life is there own.
There are some instances where a helmet would save you from a fall and there are some where it wouldn't. There are people out there that choose to wear them and there are people that do not. How does someone not wearing a helmet affect you personally? That's the question I usually ask people who question me about not wearing a helmet.