groupthink
n. a strong concurrence-seeking tendency that interferes with effective group decision making. Symptoms include apparent unanimity, illusions of invulnerability and moral correctness, biased perceptions of the outgroup, interpersonal pressure, self-censorship, and defective decision-making strategies. Causes are thought to include group cohesion and isolation, poor leadership, and the stress involved in making decisions. [identified by Irving L. Janis]