The Kurds, who had been the seawall holding back the Islamist tide, are now being hunted by Turkey’s President Recep Tayyip Erdogan —that bouncer at the gates of hell—who is turning his country into an instrument of blackmail to be wielded against the West. But in the face of Mr. Erdogan’s cynicism, the international community is behaving like the three monkeys who see no evil, hear no evil, and speak no evil.

Western diplomats are blind to the martyrdom of Kurdish fighters they find alternately admirable and dispensable. They cover their ears so as not to hear the artillery of the new sultan, who has stretched sarcasm, insolence, and his middle finger so far as to style his ethnic cleansing “Operation Olive Branch. ” Hands over their mouths, they accept Ankara’s propaganda: Nothing happened in Afrin—nothing happened there.

Some—in Moscow—perceive in the shroud of shame that Turkish irregulars have spread over Syrian Kurdistan the price of a squalid strategic victory against Islamic State. Others—in Washington—act like suave lobbyists embracing a new plan to win the peace without having waged the war.

Elsewhere the same long and excruciating silence reigns, occasionally punctuated by meaningless words and cheap sentiments. It’s “a complex region” plagued by “incomprehensible shifts in borders and alliances.” Why should the West “risk a falling-out with Russia?” While pretending to study the tea leaves and refusing to raise their faces for fear of encountering their own cowardice, the talk-show strategists, cynics and shirkers say it makes no more sense to die today for Afrin than yesterday for Danzig.

It is the eternal tale—a classic, alas, among democracies—of the powerful betraying the weak. What is new is the Faustian bargain that the West has made with Mr. Erdogan. It’s a bargain that, quite simply, is no longer sustainable. Turkey cannot continue to exist simultaneously within NATO and outside it.

Turkey has cozied up to the Atlantic alliance while brazenly liquidating NATO’s best ally in the fight against ISIS. Mr. Erdogan has felt confident enough to make, through his ministers, outrageous statements about the massacre of the Kurds (not that any massacre occurred, mind you!) being nothing next to the colonization of Algeria, which deprives France of any right to lecture Turkey. Moreover, Ankara has deployed the most heinous jihadists, keeping them on stipends before surreptitiously sending them back into combat.

All the while Turkey poses as a civilized country that, like Switzerland, Norway or Bosnia, affirms its strategic partnership with the European Union. This sad farce has gone on too long. Unless the West comes to its senses, 2018 will live in infamy as the year that Turkey dropped an iron curtain over the Kurdish people.

What coming to our senses means today is breaking off—not freezing—negotiations on Turkey’s EU accession, dissolving the EU-Turkey Joint Parliamentary Committee that continues to operate within the European Parliament, expelling Turkey from the Council of Europe (which has, incidentally, through the European Court of Human Rights, condemned the country 2,812 times since 1959), and reopening, in a serious way, the question of whether Turkey belongs in NATO.

Mr. Erdogan leaves the West no choice. If we fail to muster this basic degree of resolve, then the horror of the massacre of the Kurds will be added to the shame of watching their killer gloat atop the ruins of our honor.

Mr. Lévy is director of the documentary films “Peshmerga” and “The Battle of Mosul.” Translated from French by Steven B. Kennedy.