I have done my own personal research on Helmet wearing.
I never use to wear one for about 40 years, started riding off road and realised I came off more than on the road so after a few near misses took to wearing a helmet off road.
Occasionaly rode my road bike without a helmet until one morning 7 years ago, as a last minute thought I put it on for a ride.
Lesson 1
A car hit me from the side [just pulled out] I woke up with the police ambulance in attendance. Needless to say a Met helmet [Tested to Snell] was totaly destroyed.
Lesson 2
Riding out with a bunch on the road and some kind soul held a gate [on a gated road] open for us, I was on the outside at the front and when he let it swing closed it neatly dropped me on the road head first. Out cold for 20 seconds or so. Destroyed another helmet again a Met.
Those 2 occasions have convinced me that to not wear a helmet where there are objective dangers is foolish.
Whan the dangers are subjective I often dont bother wearing a helmet, this also applies to when I'm climbing.