I won't use a helmet because it messes with my situational awareness because of changed acoustics, i.e. disturbs my hearing of the environment where I can't see, or don't look atm, one more piece of stuff to carry around, long hairs usually pony-tailed, etc....
Feel nonetheless relatively safe, because I never fell on my head in the few (spectacular) accidents I had, never broke any bones, always (actively) managed to land hard, or didn't even fall at all.
Imagine accelerating hard into an underpass within the flow of traffic from about 45kph to 60kph to have enough momentum
for an easy climb up. And suddenly your handlebar including stern almost hits you in the face because the stern broke.
Doing some crazy moves to keep balance while still holding the handlebar in my hands, braking, not hitting any car, or the curb. Standing, upright...
In winter, on a frozen street, light curved downslope, losing control, gliding outwards, kicking against some pole to push me back, at about 20 to 25kph, back on course. Pole OK, leg too.
Entering a roundabout at about 60kph, hitting the rubberized rear bumper of an unexpectedly braking car with my frontwheel ever so slightly, flying about a dozen to 20 meters, actively summersaulting into a position with downspread arms to absorb some energy before final impact.
Hitting hard, holding head up/forward, tingling hands and feet, but not hurt. Clothing unharmed also. (Bike was trashed unfortunately)
Tell me WHY I should wear a helmet?
Do you want us all to look like the https://en.wikipedia.org/wiki/Michelin_Man for safety reasons?