

You’re comparing two things:
-
Actually observed collective pride in nations
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Pride in hypothetical tribal bands that may have never existed
And saying the first is “silly” but the second is what we’re built for.
Understanding collective pride in its actual form is less silly than pushing into some dreamed-of past.
Various tribal structures have existed and still do (I’m a registered member of a clan, was clan secretary at one point) but Rousseau’s bands are a fantasy with no archæological basis.
I see to reason to speculate on history when we have collective pride visible in our daily experience. Especially not to say the former is valid and the really-experienced one isn’t.