> groups proposing to be built of smart people are often as not built of over-opinionated pretentious people who've come to believe they are intelligent through one way or another

Dunning-Kruger societies.

I used to associate with a bunch of people who self-identified as "being smart". Trying to fit in led me to form the terrible habit of never saying "I don't know".

I've since met a number of genuinely smart people, and they are typically driven by curiosity and delight in learning, not pretension.