Despite what you might have learned in Economics 101, people aren’t always selfish. In politics, they’re more often groupish. When people feel that a group they value — be it racial, religious, regional or ideological — is under attack, they rally to its defense, even at some cost to themselves. We evolved to be tribal, and politics is a competition among coalitions of tribes.
The key to understanding tribal behavior is not money, it’s sacredness. The great trick that humans developed at some point in the last few hundred thousand years is the ability to circle around a tree, rock, ancestor, flag, book or god, and then treat that thing as sacred. People who worship the same idol can trust one another, work as a team and prevail over less cohesive groups. So if you want to understand politics, and especially our divisive culture wars, you must follow the sacredness.
from jonathan haidt’s, The Righteous Mind :: Why Good People Are Divided by Politics and Religion.