Americans were already polarized by politics, race, ethnicity and class before the Israel-Hamas war impassioned and divided us further. More than any conflict in living memory, this war has led people all over the world — even those without religious or cultural ties to either side — to square off, to demand bloody revenge and to denounce others who disagree with them.

On U.S. campuses, for example, there are professors who have posted such comments as, “Israelis are pigs. Savages. … May they all rot in hell.” Separately, there have been anonymous threats in university forums against all Jews so gruesome that some students are now afraid to walk to class alone.

At the same time, some pro-Palestinian student groups have been banned from demonstrating by their universities, such as Columbia. Individual students — including Harvard students in campus organizations that signed a letter blaming Israel for Hamas’ massacre of at least 1,200 people in Israel on Oct. 7 — have been denounced as “antisemites” by “doxxing” trucks emblazoned with their names and photographs. The trucks have parked at their universities and in front of their homes, for relentless excoriation.

Though the First Amendment of the U.S. Constitution makes it lawful for Americans to express almost any opinion about the war, such expression is now constrained by private citizens using extralegal methods, such as the doxxing trucks (created by the conservative activist nonprofit Accuracy in Media) or the threat of losing one’s job.

Several prominent figures, including David Velasco, the editor of the prestigious art magazine Artforum, and Michael Eisen, the editor of the online science journal eLife, have been dismissed from their positions for making public statements sharply criticizing Israel’s conduct of the war.

Meanwhile, rhetoric that is both very different and much worse — hateful, violent and even genocidal — is flourishing, online and offline.

One of the many problematic results is the collapsing space for dialogue and moderate opinions. More than ever, it is vital for leaders to model and teach civil dialogue. A basic tool for doing this is empathy.

A meme that has been circulating online says it is OK to empathize with civilians on both sides of the Israeli-Palestinian conflict. Surely, it is more than OK; it is necessary — and it is Christian.

Thoughtful leaders can make space for dialogue by understanding and undermining rhetoric that tends to stamp it out. At the Dangerous Speech Project , a research team I founded, we study language that inspires mass violence and the best ways to make it less effective without impinging on freedom of expression.

We define this “dangerous speech” as any form of expression, including words or images, that can increase the risk that its audience will condone or participate in violence against members of another group.

I coined that term after noticing striking similarities in the language used by malevolent political leaders to stir up followers in the months and even years before an eruption of mass violence. We saw it, for example, before and during the 1994 Rwandan genocide.

Typically, this rhetoric describes another group of people as posing a mortal threat to an in-group. Though “hate speech” is a more familiar term, we avoid it since the operative emotion is not hate; it is fear. It could also be called “fear speech. (Also there is no clear, consensus definition for “hate speech.”)

Rhetoric that precedes mass violence shares characteristic patterns — what we call hallmarks of dangerous speech — in entirely different countries, cultures and even historical periods. These hallmarks include dehumanizing people in another group by comparing them to vermin, pests or disease; suggesting that members of the out-group can pollute or contaminate the in-group; and attacking members of the in-group who are sympathetic to (or insufficiently hostile to) the out-group as traitors.

Since it isn’t natural for people to condone or commit mass violence or even to hate members of other groups, “you’ve got to be carefully taught,” in the words of the song from the musical “South Pacific.” My colleagues and I believe that dangerous speech is a tool for doing that, so we have been studying it for a decade.

There is some good news. What we’ve found is that just as influencers and leaders can incite their followers to murderous rage, they can also turn them against it. Leaders are vital, since the power of a message — the extent to which people believe and act on it — depends greatly on who speaks or writes it. Some political and faith leaders are taking eager advantage of the Israel-Hamas war to fan hatred and fear, of both Jews and Muslims. Therefore, it’s all the more important for other leaders to protect dissent, compassion and constructive dialogue with what we call “counterspeech.”

Here are three steps for that:

First, identify speech that is hateful or dangerous. Gauging which speech is dangerous isn’t a science. It’s an educated guess about which speech will make people more likely to condone or commit violence. At the DSP, we use a simple five-part analytical framework for making systematic guesses.

Second, distinguish dangerous speech from speech that is not, even if it is distressing or offensive to others. In the current public discourse, in which people’s use of particular words and phrases is often seized as a weapon to attack them, it is especially important to define boundaries carefully (for example, between dissent and incitement).

Third, if you lead a congregation or have another role that allows you to influence people, practice compassionate discourse and protect space for it. For instance, encourage people to empathize with grieving survivors on both sides of the war.

In public and private discussions, dissent or criticism is too often conflated with hate or incitement or with allegiance to the other side. For example, criticism of Israel and its siege or bombing of Gaza is not inherently antisemitic, nor does it constitute support for Hamas. Some who are criticizing the war are also antisemitic; others are not. It’s important to look at a variety of people’s public statements, not just one.

Eisen, the scientist who was removed as editor of the journal eLife, had retweeted The Onion’s satirical post “Dying Gazans Criticized For Not Using Last Words To Condemn Hamas.” One of many furious responses to his tweet demanded, without irony, “Do you condem Hamas? Do you have the courage to answer this simple question?”

The implication was that Eisen is a Hamas sympathizer, and like many such exchanges over the terrible weeks since Oct. 7, the response left no room between uncritical loyalty to Hamas and uncritical loyalty to the Israeli government.

The day after his Onion post, Eisen explained: “Every sane person on Earth is horrified and traumatized by what Hamas did and wants it to never happen again. All the more so as a Jew with Israeli family. But I am also horrified by the collective punishment already being meted out on Gazans, and the worse that is about to come.”

His critics were not appeased. In this fraught environment, empathy and criticism can be made to look like betrayal.

That is an opportunity for leadership, and some are already taking it. After Velasco was fired from Artforum and four other staffers resigned in protest, the remaining editorial staff published a new statement.

“As discourse becomes increasingly polarized,” they wrote, “the publication of carefully edited, historically informed, and factually accurate criticism that draws on a range of international perspectives remains our goal.

“We have no desire to shut down conversations around the October 19 open letter calling for a ceasefire in Gaza. We are committed to defending political expression, debate, editorial freedom, and independence.”

Theirs is a useful credo as we grapple with the war and our own national conflicts — for example, during our forthcoming elections. Political violence has been increasing dramatically in the United States, and now violence against Jews and Muslims is also rising. Dangerous speech is already taking a real toll. We must stop it from doing more damage.

More than ever, it is vital for leaders to model and teach civil dialogue.