No, that's purely a comparison between a serious accident cost and a fatal accident cost and has nothing to do with what caused the death (or what the mode of transport was for that matter), I just put it up for sake of comparison between the two.
I don't think you can argue helmets haven't saved lives, but then that's not the debate here is it really, just whether it should be compulsory or not. I have ridden without a lid (youthful demo runs and funeral processions with a large amount of compatriots likewise shod) but I still felt vulnerable.
Just for the sake of debate, let's say wearing a helmet is like an MOT, a minimal standard of safety we all have to comply with
I know that's not a great analogy
I understand the contradictory nature of saying helmet yes, clothing 'up to you'