Why is American politics so dysfunctional? Whatever the deeper roots of our distress, the proximate cause is ideological extremism: Powerful factions are committed to false views of the world, regardless of the evidence.

Notice that I said factions, plural. There’s no question that the most disruptive, dangerous extremists are on the right. But there’s another faction whose obsessions and refusal to face reality have also done a great deal of harm.

But I’m not talking about the left. Radical leftists are virtually nonexistent in American politics; can you think of any prominent figure who wants us to move to the left of, say, Denmark? No, I’m talking about fanatical centrists.

Over the past few days we’ve been treated to the ludicrous yet potentially destructive spectacle of Howard Schultz, the Starbucks billionaire, insisting that he’s the president we need despite his demonstrable policy ignorance. Schultz obviously thinks he knows a lot of things that just aren’t so. Yet his delusions of knowledge aren’t that special. For the most part, they follow conventional centrist doctrine.