I would argue that most adults do choose their associations in large part based on IQ, but they don't acknowledge it or even realize it because the overlap between IQ and what people find interesting is so great. How many low-IQ physics Ph.D.s do you honestly think there are? My son found most of the kids he knows around his age who might be considered "intellectual peers" by participating in a community theater group doing Shakespeare productions. The "shared interest" was also a filter that selected in favor of higher IQ.
This was kind of my point. Mensa struck me as a catch-all for those who didn't find a group such as the Shakespeare group or go into the physics profession, etc.
Given that one of my interests is in the realm of economic analysis (theoretical) and macro-trend stock trading (practical), I don't have an in-person group in my small metro area. Lots of people to talk to, but, given my topsy-turvy look at the market (I like bear markets better than bull markts), you just aren't going to find many people except online.
If I went to NYC, I would find plenty of such people. And it would be a group that was pre-selected for I.Q.
