The arc of the moral universe is long, but, as you may have heard, it bends toward justice. This is the elegant statement Martin Luther King Jr. assembled from the musings of a nineteenth-century Unitarian minister. It’s a hopeful thing. The idea is that, over time, good will prevail over evil. In the bedtime story America likes to tell herself, we are always forming a more perfect union.

It does seem that way sometimes. In my lifetime, gay men and women have gone from being persecuted and kept in the closet to living openly and legally marrying whom they like. Something that simple shouldn’t have taken so long, but still, it would be hard to come up with a stouter example of things getting better than that.

Things have gotten better for Black Americans over the same time period, too, although the bar for improvement was originally set on the ground. Much of the time, I openly marvel that white people aren’t being murdered in their beds more often in this country—it speaks better of the non-white races than the white—but life is measurably better than it was in the Jim Crow era.

Which is a lesson in itself, because Jim Crow was the perfect example of people looking at that arc starting to bend toward justice, snapping it the hell off, and impaling a whole race of people on it. Slavery may have been our original sin—well, that and the attempted extermination of the original residents—but Jim Crow was one sustained era of deliberate, unmitigated terrorism designed to stamp out a hopeful Reconstruction.

That’s one thing to pay attention to, if you’re in the more-perfect-union fan base. Things can get markedly better, more just, for a lot of people, but it doesn’t mean it’s going to stay that way. We have to watch for the backlash. It’s a killer.

All it takes is a demagogue, or a whole party of them, explaining how winning freedom for one set of people takes away freedoms from other people, which it doesn’t, and out comes the ugly. There is nobody in this country who will be harmed by kindness and tolerance shown to transsexuals, but by God (usually) it’s easy to direct ordinary citizens to lay waste to the public schools over such kind consideration, and to motivate the foot soldiers on their fringe to stomp them into snot. It’s easy to get them to imagine Black history isn’t American history—when it’s the epitome of American history—and start storming the libraries over teaching children the truth.

It’s child’s play to get professed Christians to disavow the Golden Rule.

You’d think the world would have learned its lesson after Hitler. You’d think some things are so important they stay learned. They don’t. It took only a few decades before we saw the rise of another friendless man with rot in his heart, and hear him refer to immigrants as vermin. To Black people as thugs and terrorists. To celebrate dictators and assassins. And to be worshipped for the audacity of being loathsome, right out loud.

I didn’t understand how the Holocaust could have happened the first time. I couldn’t imagine the world would see the like of Nazis ever again. We’re supposed to have learned.

I didn’t think we’d be dealing with measles again either. But stupidity and gullibility are highly contagious.