Following WWII there was much psychological research into how otherwise ordinary people could commit such atrocities. The most famous experiment is probably the Milgram experiment in which people who told to administrate electric shocks to another person by an authority figure in a white lab coat. So imagine this: You are told that you are going to be part of a medical experiment which aim is to test a volunteer’s (who is a collaborator but you don’t know that) tolerance to electric shock. You start by giving small shocks, then larger and larger. The volunteer starts screaming and iis eventually screaming that he might die. The test leader is standing behind you telling you that the screaming guy volunteered and that you should go ahead and give the shock. Would you? It turns out that 65% would.

The belief in authority is that strong.

Another less famous experiment along the same lines is the Asch experiment. In this experiment, you are admitted into a classroom together with a group of other volunteers. The test instructor comes in and draws two short lines and a slightly longer line on the black board. It is clear which is the longer line. The instructor then asks people to put their hands up if the line he points at is the longest. He points at one of the short lines. All the other volunteers put their hand up (they are collaborators). Do you? It turns out that 70% actually did.

Group influence is that strong.

Every day we are living an experiment and we have choices to make(*). The questions we have to ask ourself are: Do we believe in authority? Do we believe in the group? Are we  going along because we are afraid to disobey and do what is right or we afraid to stand out? Chances are that we are!
(*) There was also an experiment at Stanford, where one group of students where assigned the role of prisoners and another group were assigned the role of prison guards. This experiment had to be stopped!