One topic of social psychology that I found very interesting was the study of groupthink and cults. Groupthink, the emphasis on group unanimity at the expense of critical thinking, in extreme form can lead to cults, groups that exhibit intense and unquestioning devotion to a single cause. Evidence suggests that cults promote groupthink in four major ways: having a persuasive leader who fosters loyalty, disconnecting group members from the outside world, discouraging questioning of the group's assumptions, and establishing training practices that gradually indoctrinate members.
Cults have an abundance of misconceptions. One is that all cults members are emotionally disturbed. Research shows that most cult members are psychologically normal, however many cult leaders probably do suffer from serious mental illnesses. This misconception occurs because we overestimate the role of personality traits and underestimate the role of social influences. It's hard to believe the power that a group can have over a single individual and that a simple idea such as groupthink can lead to something as extreme as a cult.