“Some people don’t like other people just because they’re Jews,” declared a main character in the 1947 Oscar-winning American classic, “A Gentleman’s Agreement.” The crematoria at Auschwitz had not yet cooled down, but there were Americans who couldn’t abide the thought of Jews sharing their country clubs, neighborhoods, or college classrooms. Those were the challenges for American Jews back then, but today we no longer worry about “gentlemen.” After Pittsburgh, we’re on guard against the next lone wolf psychopath, armed with hate and bullets, empowered and validated by his invisible social media bigoted “friends.”

For us Jews it’s (still) the best of times — and, as we bury our dead in Pittsburgh, the worst of times. According to Pew, we are the single most admired religious group in America. On the other hand, the FBI confirms that we are the #1 target of religion-based hate in the United States.

Simon Wiesenthal said that “hope lives when people remember.” Let us remember who is responsible for keeping antisemitism alive in our time, lest we be powerless to resist it.

The Pittsburgh gunman is responsible for his heinous deeds. Yet such extremism does not operate in a vacuum. Here are some points to ponder after the Pittsburgh massacre recedes from the headlines. We offer them as professionals who have struggled with antisemitism worldwide for decades.

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Social media outlets like Gab market hate. Hiding behind a freedom of speech mantra, they deny any moral responsibility for the platform they offer to the worst misusers of the privilege of that freedom, eerily similar to ISIS, whose online marketing campaigns spawn lone wolf terrorist attacks on both sides of the Atlantic.

Good people used to drive the haters underground. No longer. In major capitals — London, Paris, Brussels, Copenhagen, Stockholm — it is dangerous for Jews to wear the Star of David or a kippah in public. Police and politicians look the other way as (mainly) Islamist extremists bully and pummel Jews on the streets of Europe. Important institutions are rife with winking at antisemitism, or even worse.

Malaysian Prime Minister Mahathir Mohamad calls Jews “hooked-nosed,” and boasts that he is “glad to be labelled antisemitic.” On a recent visit to the UK, Mohamad was welcomed to Imperial College and Oxford by the heads of these institutions. Jeremy Corbyn’s Labour Party is awash with Jew-hatred, but he could be the UK’s next leader.

An unholy alliance of terrorist groups like Hamas and Hezbollah, funded by Iran, uses antisemitism as a tool to turn the world against Israel. Their propaganda has found enthusiastic support in academia and even churches, so that today over 150 million Europeans believe Israelis treat Palestinians the way Nazis treated Jews. Young Americans hear much of the same on campuses dominated by progressives who detest power and “privilege,” especially of Israel and the United States.

Anti-Zionism has flourished as a tool for gutless Jew haters: “We don’t hate Jews. Only Zionists.” Now, there is lots of room to criticize Israel without being antisemitic in the slightest. But when that criticism demonizes or subjects Israel to a double standard, the road to antisemitism has been crossed.

Syria, Iran, Nigeria, Myanmar, China — millions are dying, or living in exile, or incarcerated in internment camps for their religious beliefs, but the lion’s share of UN resolutions contemptuously pile on the Jewish state. The Jewish people’s historic links to their key religious sites have been denied.

For close to two thousand years, the Church (followed by various churches) taught and encouraged antisemitism. That has changed for the better in some denominations, and in some areas. But old attitudes die hard. Rather than show special sensitivity to Jew-hatred, some churches still feed into it. The over-the-top hostility of some church groups to Israel is a case in point.

The Quakers, who risked their lives to save Jews during the Holocaust, are today no friends of Jews. Mennonites in South America actively aided Hitler in his campaign to demonstrate pure Aryan superiority. (Their contempt for Israel translates in the popular mind into a rejection of Jews and Judaism.) Many other church groups aid and abet the virulent Jew-hatred of Palestinian groups by standing by them as allies, without calling them out for the antisemitism constantly spewed in their mosques and textbooks.

And, of course, there is the right-wing antisemitism of the Pittsburgh murderer, encouraged and similar to what we saw in Charlottesville.

Tragically, the Pittsburgh synagogue massacre is not — cannot — be a one-off, any more than 9/11 was, even if never repeated. It will change the way Jews live for the foreseeable future. Houses of worship, citadels of peace, will look more like TSA portals to airports.

So things are bad and could get even worse. What can we do to try to stem the tide?

Don’t underestimate the sheer volume of age-old Jew-hatred. It did not disappear after the Holocaust. It never disappeared from polite society. When William Buckley, Jr. wrote his series on antisemitism (“In Search of Anti-Semitism,” National Review, Dec. 30, 1991) he quoted McGeorge Bundy, an adviser to two presidents, and a former dean of Harvard, in explaining that lots of people still hate Jews just because they are there. Many don’t even understand their own bias.

People must stop pretending that Jews do not need a country of their own — that they are perfectly safe in the world’s democracies. They are not. Untold millions of Jews would have survived the Nazi Holocaust had a Jewish state existed then. Today, flourishing Israel is hope to more that six million Jews, including thousands who have recently fled France and England. When you deny the legitimacy of the Jewish state, you are denying the right of Jewish survival.

Don’t believe the bald-faced lies, like Israel is an apartheid state, or that the hordes violently attacking Gaza’s border fence are “peaceful demonstrators.” Do your own independent search for truth that extends beyond Twitter and YouTube. Don’t believe BDS boycotters of Israel when they claim that they are peace-seekers. They aren’t. Their goal is to demonize and ultimately get rid of the Jewish state.

We must also understand what constitutes antisemitism. Many governments have adopted the International Holocaust Remembrance Alliance definition of this hatred, which has eleven components: particularly noteworthy are ones against claiming that the existence of a state of Israel is a racist endeavor; requiring of it [Israel] a behavior not expected or demanded of any other democratic nation; using the symbols and images associated with classic antisemitism (e.g., claims of Jews killing Jesus or blood libel) to characterize Israel or Israelis; and drawing comparisons of contemporary Israeli policy to that of the Nazis.

Finally, go to a Shabbat service in your neighborhood. Get to know us beyond the bagels-and- lox level. The greatest disinfectant to negative stereotypes is to meet the other.

Simon Wiesenthal was once asked: “Were you surprised by how many Nazis there were,” he answered that he was surprised “only by how few anti-Nazis there were.”

We need healing and we need friends. And we need America and Americans to be those friends.

Rabbi Abraham Cooper is associate dean and director of global social action for the Simon Wiesenthal Center. Rabbi Yitzchok Adlerstein is the Center’s director of interfaith affairs.

A version of this article appeared in The Christian Post.