In 1391, a wave of violence against Jews swept through Christian Spain. In its wake, thousands of Jews converted to Christianity. The following century saw more conversions as Spain became increasingly hostile toward its Jews. Some of these conversos—as they were called—quickly returned to Judaism after the violence abated; others lived outwardly as Christians while practicing Judaism in secret; others sought to assimilate completely into Christian society; and still others followed intermediate courses of action. The status of the conversos in Jewish law produced a substantial body of rabbinic scholarship, which is the subject of a recent book by Dora Zsom. Andrew Apostolou writes:

The question of how we deal with estranged Jews turns out to be an enduring one. Similar groups to the conversos emerged in the 19th and 20th centuries in such different societies as Germany, the Soviet Union, and now the United States. The debate over how to define Jewish identity in the new state of Israel, for example, led Ben-Gurion in 1958 to write to rabbis across the world to seek their opinion on “who is a Jew?” . . .

These contemporary concerns bring us back to the question of how much impact the rabbis had. [Dora] Zsom’s narrow focus means that she cannot draw out the effect of their decisions. What we know, according to Arthur Hertzberg in his classic entry in the Encyclopedia Judaica on “Jewish Identity,” is that those conversos who wanted to become Jews often forced the gates open: “the determining act was their willingness to become part of the Jewish community, and all the halakhic doubts of rabbinic authorities remained theoretical in the face of acts of return.”

Two extraordinary events demonstrate something important about Israel’s most fervent adversaries. One was a speech given at something called The People’s Forum (funded generously by Goldman Sachs), which stated, “When the state of Israel is finally destroyed and erased from history, that will be the single most important blow we can give to destroying capitalism and imperialism.”

The suggestion that this tiny state is the linchpin of a global, centuries-old phenomenon like capitalism goes well beyond anything resembling rational criticism. Even if Israel were guilty of genocide, apartheid, and oppression—which of course it is not—it would not follow that its destruction would help end capitalism or imperialism.

The other was an anti-Israel protest that took place in front of New York City’s Memorial Sloan Kettering Cancer Center, deemed “complicit” in Israel’s evils. At organizers’ urging, participants shouted their slogans at kids in the cancer ward, who were watching from the windows. Given Hamas’s indifference toward the lives of Gazan children, such callousness toward non-Palestinian children from Hamas’s Western allies shouldn’t be surprising. The protest—like the abovementioned speech—deliberately conveyed the message that Israel is the ultimate evil and its destruction the ultimate good, cancer patients be damned.

The fact that Israel’s adversaries are almost comically perverse does not mean that they can be dismissed. If its allies fail to understand the obsessive and irrational hatred that it faces, they cannot effectively help it defend itself.