And we could save a lot of people if they put on helmets to walk down stairs, and yet I don’t see anyone saying that people are stupid not to wear them.

And your friend, if he drives at 30mph, of course he has to wear a helmet, but the subject is not a sporty practice of cycling, but bike commuting. And helmets does not protect you from a shitty infrastructure and tank-like cars that run you over, so maybe it would be good to stop insulting people and bring some nuance to this debate.