Demonization (or 'demonisation', as it is spelt in British English) is an argumentative strategy, often employed in political contexts, whereby one group consistently describes a rival group as beings of pure evil who want nothing more than their enslavement, destruction, or corruption. Such a strategy is very good for whipping up lynch mobs, quelling internal strife 'in the face of the common threat', and stifling the usual twinges of conscience most people experience when mistreating others. This sometimes requires the use of otherism beforehand, to make people view the targeted group as an "other."
Another recent trend is the demonization of people of Hispanic descent in North America by some US politicians as somehow not being as deserving of an equal right to domicile as their northern-European descended cousins.
Conservative talk radio depends on the demonization of liberals (and even moderates) for most of their material.
One of the most common types of demonization in Internet debates is referenced by Godwin's Law - that being, comparing the opposing person/group to Hitler and/or Nazis.
 See also
- Evil baby-killing America-hating Liberal
- Evil Neo-Nazi Fascist Minority-hating Conservative
- Evil "they're all jihadists" Muslim-hating bigot
- Evil Liberal Science Conspiracy
- The Evil Jew (antisemitic stereotypes)