The Righteous Mind: Why Good People Are Divided by Politics and Religion
The most satisfying answer I've read to the title question.
Reading this is looking behind the curtain of life. Maybe that's what all good psychology does? Maybe that is psychology? In any case, The Righteous Mind makes a hell of a good case for why we act the ways we do, and how that then gets articulated as what we call 'politics'.
It gives one of the best arguments I've heard for the divide among the left and the right. Or at least it's part of the story. If it is partial, then its tenants are a big part of that story.
1. Plato said reason rules the heart. Franklin said the head and the heart are a team. Hume said the head follows the heart, justifying it and building a model of the world that suits the passions. Heidt makes a case that Hume was right. Intuition isn't built from reason. Reason tends to follow built-up intuition.
2. Political preference is influenced by various moral interests: Care, Liberty, Authority, Loyalty, Sanctity. The degree to which these are combined in any one person tends to highly correlate with their political "team".
3. Once you're first draft, gene-influence preferences lead you to a political team, your reinforced intuitions lead you to more and more mental cement. And once you're cemented with a perspective within a group, feedback from that group keeps your stuck. Our need to be in a tribe keeps us blind.
This analysis works in both political directions, and it's elaborated in such a mind opening way.
Learn your elephants and love your neighbors.