One way is to acquire habits of thinking and discourse that reduce the Other Side to cartoonish villains. For example:
Essentializing: Characterizing a quality or trait as fundamental to a particular person or type of person or defining a person by their worst behavior. Example: "Public figure ‘X’ is a sexual predator".
Mindreading: assuming one knows someone else’s thoughts, feelings and motivations – that is, the “real” reasons for what they say, think and do. Example: “It All Comes Down to Race: Your opinions on health care reform, taxes, and even the president’s dog …”
Damning the Inner Other: a propensity to focus on and condemn the beliefs, motivations, biases, and inner life of out-group members and political opponents, as in accusations that rich people only give to charity out of self-interest.
In-group bias: a pattern of favoring members of one's in-group over out-group members and of seeing in-group members as unique individuals and out-group members as representative of group stereotypes.
Narratives of Blame: Simplistic stories that connect past events to current inequities, often leaving out a bunch of relevant data. Example: Past Housing Discrimination Is to Blame for Current Income Disparities.
Scapegoating: when individuals and groups settle on a specific target to blame for their problems. Example: Americans Blame Corporate Greed for Moral Decline
Dehumanizing: Dehumanizing rhetoric downplays the individuality and humanity of others, often by giving them labels like predators, snakes, cockroaches, parasites, and cancers.
Dismissive: showing that you think something or someone is not important and not worth considering. Example: reducing criticism or disagreement to a matter of one’s critic being “inconvenienced”, as in Activists work for a greater good, which may just inconvenience you.
These are a few of the ways we shore up the certainty of our convictions and justify not considering other points of view. If the Other Side is morally bankrupt and devious, why bother to listen to what they have to say?
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*Yeah, the examples are mostly from the left side of the equation. What can I say? I live in the heart of Progressive America and these examples are what come to mind.