Mental virus
Stereotype is a mental virus spreading among human minds, which forces a person to do certain action without reasoning it's consecuences. Virus transfers in the framework of social relations. In other words this procedure can be called "taking an example". The only special feature is, that this happens without consciousness. Condition of no consciousness is usually maintained by stress or other emotional disorder. In such condition people acquire information without critical thinking.
Examples. Person sufferred violence in childhood is most likely to become violent, when grown up. Person in love, if deceived by loved one, will deceive his future partners with similar to first case feelings the same way it was deceived once in a first case. Such virus uses both general socialisation patterns (learning a behaviour by taking an example) and a "Revenge" psychological feature of a human.
Virus can be exterminated by affecting "Taking example" and "Revenge" psychological features. See Bible, Koran and other religious scriptures for further instrucions on protection against psychological viruses.