Why do we constantly choose to believe the most unbelievable story of all; usually the official one?
Most people prefer to believe their leaders are just and fair even in the face of evidence to the contrary, because once citizens acknowledge that the government under which they live is lying and corrupt, citizens have to choose what they will do about it. To take action in the face of a corrupt government entails risks of harm to life and loved ones. To choose to do nothing is to surrender one's self-image of standing for principles. Most people do not have the courage to face that choice. Hence, most propaganda is not designed to fool the critical thinker but only to give moral cowards an excuse not to think at all.
The Nazis, Fascists and Communists were political parties before they became enemies of liberty and mass murderers.