Put very simply, groupthink is a psychological phenomena where group harmony and unity are encouraged to the degree that outside opinions or disagreement is disregarded. Originally coined in 1952 by William H. Whyte, Jr., it was researched and more thoroughly defined by psychologist Irving Janis in the 1970s. "The term refers to a deterioration in mental efficiency, reality testing and moral judgments as a result of group pressures." (I.L. Janis, Psychology Today, Nov. 1971) (More on deterioration of mental efficiency in a later post.)
In general, when pressure to conform is strong, members don't even consider possible alternatives. In my case, any objections were kept to ourselves, as voicing any dissent was considered "doubting" or disloyalty, which were strongly discouraged. Ideas presented from outside sources were not taken seriously. Outsiders were stereotyped as "systemites" - members of society at large and subject to the "system" from which we deemed ourselves free. So of course, no alternative lifestyles were even considered.
We cultivated the belief in the rightness of our cause (the chosen and called of God), and "gave no thought to the morrow" nor to the eventual consequences of our choices and decisions. In came the delusions of the importance of our work. Membership in the group was thought to be more important than anything else.
In short, groupthink led to a very distorted sense of reality.