Groupthink

Groupthink is a term coined by psychologist Irving Janis in 1972 to describe one process by which a group can make bad or irrational decisions. In a groupthink situation, each member of the group attempts to conform his or her opinions to what they believe to be the consensus of the group. This results in a situation in which the group ultimately agrees on an action which each member might normally consider to be unwise.

Definition taken from http://www.co-intelligence.org/