More than once during the summer, I heard well-established British Jews saying, “For the first time in my life, I feel afraid.” Twenty years ago, launching a program to strengthen Jewish continuity across the generations, I published a book titled, “Will We Have Jewish Grandchildren?” Today, Jews are beginning to ask, “Will we have English grandchildren?”

And Jews are leaving. A survey in 2013 by the European Union Agency for Fundamental Rights showed that almost a third of Europe’s Jews have considered emigrating because of anti-Semitism, with numbers as high as 46% in France and 48% in Hungary. Quietly, many Jews are asking whether they have a future in Europe…

Hatred, when taken into the public domain, is singularly difficult to justify, which is why anti-Semites have always sought vindication from the highest source of authority in the culture. In the Middle Ages, it was religion. In 19th-century Europe, it was science. German anti-Semitism was based on the so-called “scientific study of race” and social Darwinism, the doctrine that in human history, as in nature, the strong survive by eliminating the weak.

In the era since World War II, the great authority has been the Enlightenment ideal of human rights. That is why the new wave of anti-Semitism was launched at the U.N. Conference against Racism at Durban, South Africa, in the summer of 2001. There Israel was accused of the five cardinal sins against human rights: racism, apartheid, crimes against humanity, ethnic cleansing and attempted genocide.