Mensa is mostly just a club for people who are disproportionately cultural outsiders. A lot of them have the same interests that are harder to come across in regular day to day life.
It's not so much a circle jerk of "we are so smart" as it is a circle jerk of "no one else wants to play SET! with me".
I was a gifted child and in the 1980s before the internet it gave me a community of adults who had a life of the mind and were for the most part professionals, whose experiences I really benefited from a lot from as a 12 year old.
I don’t know if the IQ test (Advanced Raven Matrices) was a useful bar — there were lots of smart people who weren’t in Mensa — but there were enough smart people in it that I found a community of like minded folks. It’s not easy for kid to find a community like that but I did.
Most people think Mensa is full of self aggrandizing nerds but that wasn’t my experience (it varies by chapter).
Mensa probably doesn’t have a purpose today but pre Internet it did, even if by accident. I don’t think IQ is a useful membership criterion due to sheer arbitrariness but sometimes arbitrary groupings of people can work.
I would also say that people who have a knee jerk negative reaction against Mensa are no more likeable than the socially inept segment of the Mensa membership they disparage. They have the same kind of puffed up pride that they dislike.
It's not so much a circle jerk of "we are so smart" as it is a circle jerk of "no one else wants to play SET! with me".