You're speaking in absolutes, so it only takes one exception to refute your premise.
FWIW, when Mensa has an impressive speaker the discussion of a topic can be incredible. People don't hold back on questioning and disagreeing because of a fear of offending anyone with non-mainstream thoughts. A good dinner group where the discussion can be a lot like it gets on FR....going in all directions with a lot of give and take. Then there's its function as a sort of family for those who don't have close family ties or terrific social skills in large fake social environments.
Have you ever been to a Mensa meeting?
Thank you. If all that the really, really intelligent people in this world did was to sit around and talk about themselves, we’d never have gone to the moon or split the atom.