Vaccines, politics, religion. This explains everything.
The wiki on inolculation theory:Media as a Vaccine against Critical Thinking
Human communication is of a persuasive character, since the perspective to determine the difference between fact and opinion differ according to sociological and cultural backgrounds. Media sets the ground for building stereotypes by imposing the ideas to the recipients. It makes media a tool for persuasive communication thus producing the effects of what a vaccine injection might do to a human body. As language is one of the most used tools in media, this stealthy persuasion operates on a subtle “antigens” infiltrated in the context of the media text. “Mind vaccinating” recipients by media eventually can lead to stereotyped perceptions and produce prejudice. In this metaphor vaccine antigens offer a persuasive perspective on reality immune to other perspectives but that one that is imposed by media. If a recipient in the communication process understands the threat then the persuasive effects are lessened as is explained in inoculation theory.
Inoculation Theory was developed by social psychologist William J. McGuire in 1961 to explain more about how attitudes and beliefs change, and more importantly, how to keep original attitudes and beliefs consistent in the face of persuasion attempts. Inoculation Theory continues to be studied today by communication, social psychology, and social science researchers. The theory has been assessed in varied context, including politics (Pfau et al., 1990), health campaigns (Pfau & VanBockern, 1994), and marketing (Compton & Pfau, 2004), among others.