Cults thrive on our vulnerabilities, and a good demonstration of just how vulnerable we all are was given in a series of experiments conducted by social psychologist Solomon Asch in the 1950s.
In this video you can watch a modern reproduction of the experiment. All involved are “confederates”, except for the one person who is the unsuspecting subject.
Asked about a simple obvious question, everyone will give correct answers at first, but then will start to give unanimously wrong answers. Again and again.