In all my Tribes Collection a few years ago, I don't think I ever spoke to one of the most obvious sources of evidence: sports teams.
We root for a team or set of teams, usually on a geographic basis. There is usually nothing inherently superior about those teams that is not easily explained by some factor that has no relation to us and our interests: a superior coach or player for a decade, an owner willing to spend more money. Yet we have an attachment that causes us to take our team's side in all disputes. It was a terrible call. There was no bounty on opposing players. Our opponents play dirty. The refs are homers. We are certain that our John Smith is more deserving of going into the Hall of Fame than all the other John Smith's with similar careers*. We believe UK just deserves our support for some reason, and are sure that its players are more solid citizens than those thugs over at Duke. If we went to a school we root for it decades later, for no reason whatsoever.
(That this attitude can be combined with the belief that the management and coaching of our favorite team is unusually stupid and evil is not a contradiction. It comes under the category of I can insult my brother, but you can't insult my brother.)
And some of us are not merely fans, by psycho fans, defaulting immediately to the belief Joe Pa got a raw deal, or screaming abuse at opposing players. (I've done that. It's insane.) There may be some excuse if we've got a friend or relative on the team, but in a world that seeks justice, we should accept the idea that our kid's team may have jerks and dirty players on it, and not take their side against some opposing kid who is playing cleanly. There's a code in competitive sports that says you defend a teammate. Well, loyalty is a virtue, and it's a good thing to teach. But it's not the only virtue, and it can go bad quickly. I think it was Seinfeld that used to reference "Rooting for laundry." Not that there's anything wrong with that.
Most reasonable people can indeed step back and say "Y'know, if I had been born twenty miles north I would be rooting for a different Carolina today. Funny." We can even laugh wryly at ourselves about such things. We get a little worried about people who actually can't be this objective, even after the season is over. Such folks bring us the deaths at European soccer stadiums.
So, when I talk about our political tribalism, our rooting for our guy even when he's wrong, our gamesmanship that seems to have left the core ideas - as opposed to slogans and stereotypes - behind years ago, while our furious support goes on endlessly, remember that we are indeed capable of this. I think I have acknowledged that conservatives do this a lot, only partially seeing it. I think I have focused my criticism on liberals around the fact that they don't see it at all, and believe they are the one group above this. But maybe that's just fandom. Were I to face the truth fearlessly I might see it differently.
Take a moment to recognise that you are capable of this favoritism for illogical, accidental reasons, and that sports is your example. (You non sports fans, try harder. There's something.)
*I was going to use Dwight Evans and Darrell Evans for this, but looking at the numbers, Dewey really was better, so it weakens my point. I say this with no pro-Red Sox bias whatsoever.