Earlier this month, my fellow liberals despaired when the Supreme Court upheld the right of a Colorado baker to refuse service to a gay couple. In the America we envision, everyone is equal. So we shouldn't allow a private enterprise to discriminate against customers.

Unless, of course, those customers are members of the Trump administration.

Last Friday, a restaurant in Lexington, Va. asked White House press secretary Sarah Huckabee Sanders to leave the premises. Owner Stephanie Wilkinson cited Sanders' defense of President Trump's zero-tolerance immigration policies and his efforts to bar transgender people from the military, adding that several employees at the restaurant were gay.

So let's recap: If you refuse service to gay people, that's a terrible thing. But if you won't serve someone whom you think discriminates against gays, that's perfectly OK. "This feels like a moment in our democracy when people have to make uncomfortable actions and decisions to uphold their morals," Wilkinson told a reporter.

She's right. But democracy also demands that we uphold shared norms of tolerance and decency, which are under huge strain at this moment. We need to rally around them, no matter how uncomfortable it makes us. As Michelle Obama said at the Democratic National. Convention, "When they go low, we go high."

That means resisting the easy temptation to dehumanize our foes, which Sanders' own boss has done so much to accelerate. To Donald Trump, political opponents aren't simply people who disagree with him. They're losers, dummies, wackos, and psychos. They don't deserve empathy, recognition, or respect.

The decision to remove Sanders reflected a similar spirit. If you refuse service to someone, like the Colorado baker did, you're not simply registering a different point of view. You're also questioning the customer's basic humanity, their right to exist on the same plane as you do.

To be fair, Wilkinson showed admirable politeness when she booted Sanders, asking Sanders to step outside before delivering the bad news. Wilkinson also generously refused to accept payment for Sanders' eight-person party, which had already been served dinner.

The protesters hounding Homeland Security Secretary Kirstjen Nielsen haven't shown such restraint. They confronted Nielsen last week at a Mexican restaurant in Washington, yelling, "End Texas concentration camps." In a separate incident, demonstrators gathered outside Nielsen's home and blasted audio of crying migrant children who have been separated from their parents at the U.S.-Mexico border.

And last Saturday, Rep. Maxine Walters (D., Calif.) urged cheering supporters to confront other Trump administration officials in public spaces. "They're not going to be able to go to a restaurant, they're not going to be able to stop at a gas station, they're not going to be able to shop at a department store, the people are going to turn on them, they're going to protest, they're going to absolutely harass them until they decide that they're going to tell the president, 'No, I can't hang with you, this is wrong this is unconscionable and we can't keep doing this to children,'" Waters told a Los Angeles rally.

That's a fantasy, of course. Nobody seriously believes that this type of action is going to persuade anyone, least of all members of the Trump administration. Instead, it's going to lock us even more firmly into our respective political camps. And it will generate yet more uncivil behavior, on every side of the aisle.

Witness the hateful vitriol directed last weekend at the Red Hen restaurant in Swedesboro, which has the same name as the Virginia establishment that booted Sanders and her party. The New Jersey restaurant reported at least 600 phone calls from people who had confused the two places. Many of them cursed and shouted; a few threatened to burn down the restaurant, or to harm its employees.

And when its management asked posters on Facebook to stop denouncing the Jersey restaurant, it only seemed to stoke more anger. "So you are OK with liars and traitors?" one woman asked. That tells you all you need to know about our poisoned political world right now. You're either with us or against us, part of the solution or part of the problem.

I'm outraged by the Trump administration's policies on immigration and gay rights, and I encourage everyone to protest them. The only way the policies will change is if we raise our voices.

The real question is how. If we place our opponents outside of the realm of human decency, we write off the possibility of winning them over. We make politics into a simple act of power and coercion, not of persuasion. And we echo our callous president, who has done so much to flout our best democratic traditions.

Those traditions were captured 50 years ago by the Congress of Racial Equality, one of the leading groups protesting racial segregation. When challenging a moral evil, CORE urged, demonstrators should "make a sincere effort to avoid malice and hatred." Anything less brings us down to the level of our foes.

And once we go there, we might never come back.

Jonathan Zimmerman teaches education and history at the University of Pennsylvania. He is the author (with Emily Robertson) of  "The Case for Contention: Teaching Controversial Issues in American Schools" (University of Chicago Press).