My impression is that the point of Mensa is to provide smart people who would otherwise be isolated with opportunities to interact with other smart people. Now:
So Mensa seems likely to be selecting for the following combination of attributes:
Now, of course not everyone there will fit that pattern, for all kinds of reasons. And some people who do fit that pattern may be interesting fun people capable of getting things done. But it doesn't seem like it should be a big surprise if a lot of them aren't.
Intelligent ... but not too intelligent
For statistical reasons, there are much more people with IQ 130 than with IQ 150 (or whatever is the LW average). So an organization of "IQ 130 or more" will turn out to be "IQ 130, and only rarely more".
Not especially ambitious
I'd say that the less ambitious members are more visible in Mensa, because they don't have alternatives. For example, one member of our local Mensa got currently into parliament. That seems ambitious enough to me. But he doesn't spend nearly as much time in Mensa as t...
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