Scientists are as prone as anyone else to groupthink, and stifling dissent often produces disaster. Three of the costliest policy failures in recent decades—the 2008 financial crisis, the Covid lockdowns and the campaign for rapid decarbonization—share a pathology we call the Consensus Trap. Problems began with the output of complex, unvalidated models presented as facts. Institutions and public figures under pressure to appear authoritative ignored uncertainties. Along with the press, these institutions and people became arbiters of truth, amplifying the declared consensus rather than critically assessing the evidence. Once “the science” was declared, dissent was treated as misconduct. In all...