People will put on some shorts, a tanktop and some flip-flops, get on their bike, and ride similar speeds to that of someone on a motorbike wearing full safety gear. All while surrounded by vehicles which weigh tonnes and with the most likely surface their head will hit being the curb or some concrete. It's stupid.
I mean, seriously. Hit your self in the head with a brick or an iron bar. You're likely to hurt yourself badly even if you do it lightly, let alone full force.