Glenn Harlan Reynolds

"What if I told you," asks a Matrix-themed photo-meme that has been circulating on Facebook, "that you can be against cops murdering citizens and citizens murdering cops at the same time?"

Judging by the past few weeks, this really is a Matrix-level revelation, obvious as it may seem. We have Americans protesting because of police shootings, and we have police turning their backs on New York City's Democratic Mayor Bill de Blasio over lack of support after two police were assassinated by Ismaaiyl Abdullah Brinsley, a gunman from Baltimore who said he was seeking revenge for the choking death of cigarette-tax evader Eric Garner.

And, as blogger Eric Raymond notes, the response has been divided: "Because humans are excessively tribal, it's difficult now to call for justice against Eric Garner's murderers without being lumped in with the 'wrong side.' Nor will Garner's partisans, on the whole, have any truck with people who aren't interested in poisonously racializing the circumstances of his death."

Like this column?: Get more delivered

This is a tragedy, but not a surprise. Tribalism is the default state of humanity: The tendency to defend our own tribe even when we think it's wrong, and to attack other tribes even when they're right, just because they're other. Societies that give in to the temptations of tribalism — which are always present — wind up spending a lot of their energy on internal strife, and are prone to disintegrate into spectacular factionalism and infighting, often to the point of self-destruction.

Societies that temper those tribal tendencies, replacing them with the mechanisms of civil society, do much better. But there is much opportunity for political empire-building in tribalism, and if the benefits of stoking tribal fires exceed the costs for political actors, then expect political actors to pour gasoline on even the smallest spark.

That's pretty much what's happened in the last few months, and the results haven't been good. In America, we have both a police culture that is too quick to escalate force, and an aggressive victim culture, embodied by the loathsome Al Sharpton, that seeks to portray every police use of force, at least against members of the wrong racial and ethnic groups, as excessive.

A healthy society would stigmatize, marginalize and shun the tribalizers. Sharpton, who has incited racial violencein the past, would not have a network TV show (even on MSNBC), and would not be treated as a legitimate civil rights spokesman. Police unions, which have a history of interfering with efforts to hold officers accountable for acts that, if they were committed by civilians, would be prosecuted as crimes, would not be given a preferred political position, if they were allowed to exist at all. (Personally, I agree with FDR that public employee unions are essentially a conspiracy against the taxpayers; it's an even more significant matter when they're public employees who carry guns.)

In a healthy civil society, people can deal with others without worrying about tribalism, confident that disputes will be settled by neutral and reasonably fair procedures overseen by neutral and fair people. In a tribalized society, what matters is what tribe you belong to, and who is on top at the moment.

Healthy civil societies are a lot better places to live. They're richer, safer and more peaceful. But healthy civil societies don't provide the opportunity for political power grabs, for payoffs and for extortion that tribalized societies do. It's no wonder that so many political figures favor tribalism. The question is, how long will the rest of us allow them to get away with it?

Glenn Harlan Reynolds, a University of Tennessee law professor, is the author ofThe New School: How the Information Age Will Save American Education from Itself.

In addition to its own editorials, USA TODAY publishes diverse opinions from outside writers, including our Board of Contributors. To read more columns like this, go to the Opinion front page or sign up for the daily Opinion email newsletter.