This sort of anti-Semitism thrives where there aren’t that many Jews. The Jew is not a person but an idea, a unique carrier of transcendent evil: a pollution, a stain, a dark force responsible for the failures of others, the unconscious shame and primeval urges they feel in themselves, and everything that needs explaining. This is a form of derangement, a flight from reality even in otherwise sophisticated people.

This form of anti-Semitism cannot be reasoned away because it doesn’t exist on the level of reason. It can only be confronted with deterrence and force, at the level of fear. The challenge for Israel is to respond to extremism without being extreme. The enemy’s rabidity can be used to justify cruelty, even in cases where restraint would be wiser. Israeli leaders try to walk this line, trying to use hard power, without becoming a mirror of the foe, sometimes well, sometimes not.

In Europe, anti-Semitism looks like a response to alienation. It’s particularly high where unemployment is rampant. Roughly half of all Spaniards and Greeks express unfavorable opinions about Jews. The plague of violence is fueled by young Islamic men with no respect and no place to go.

In the current issue of The Atlantic, Jeffrey Goldberg has an essay, “Is It Time for the Jews to Leave Europe?” He reports on a blizzard of incidents: a Jewish school principal who watched a Frenchman of Algerian descent pin his 8-year-old daughter down in the schoolyard and execute her; a Swedish rabbi who has been the target of roughly 150 anti-Semitic attacks; French kids who were terrified in school because of the “Dirty Jew!” and “I want to kill all of you!” chants in the hallway; the Danish imam who urged worshipers in a Berlin mosque to kill the Jews, “Count them and kill them to the very last one.”

Thousands of Jews a year are just fleeing Europe. But the best response is quarantine and confrontation. European governments can demonstrate solidarity with their Jewish citizens by providing security, cracking down — broken-windows style — on even the smallest assaults. Meanwhile, brave and decent people can take a page from Gandhi and stage campaigns of confrontational nonviolence: marches, sit-ins and protests in the very neighborhoods where anti-Semitism breeds. Expose the evil of the perpetrators. Disturb the consciences of the good people in these communities who tolerate them. Confrontational nonviolence is the historically proven method to isolate and delegitimize social evil.