The most powerful force ever known on this planet is human cooperation — a force for construction and destruction.

The line distills a central theme in Haidt’s moral psychology: humans are uniquely capable of forming cohesive groups that can achieve feats no individual could manage alone. “Cooperation” is framed as an amplifying power—able to build institutions, knowledge, and prosperity (“construction”), but also to enable coordinated cruelty, war, and oppression (“destruction”). The quote underscores Haidt’s recurring emphasis on groupishness: our moral emotions and shared narratives bind us into teams, which can elevate collective life or turn moral certainty into a weapon. It is a warning against romanticizing solidarity without attending to the ways it can harden into tribalism.