Four Jews were brutally murdered at a French kosher supermarket, and the gunman stated that he chose the store because it was populated with Jews. Astoundingly, some hesitated to call this an anti-Semitic attack.

Karen Armstrong, an exceptionally popular writer on religion, was quoted in a Dutch blog: “The supermarket attack in Paris was about Palestine, about ISIS. It had nothing to do with anti-Semitism; many of them are Semites themselves. But they attempt to conquer Palestine and we’re not talking about that. We’re too implicated and we don’t know what to do with it.” That this highly regarded writer could not bring herself to state what the perpetrator himself admitted is evidence of the loss of a moral compass and of a trend that must be understood and challenged — a trend that includes a toxic mix.

Last week was the 70th anniversary of the liberation of Auschwitz, the death camp where more than 1 million Jews were murdered during the Holocaust. Twenty years ago, on the 50th anniversary of liberation, JCRC organized an unforgettable commemoration honoring 120 liberators of the camps who were living quietly in communities throughout Northern California. On the 60th anniversary, we honored the survivors living in our midst at a luncheon attended by 1,000 survivors and community members, celebrating the ways in which the living eyewitnesses to the horrors of the Holocaust have enriched our community.

There will be a beautiful Yom HaShoah commemoration on April 15 this year, as every year, but there will be no major community event with hundreds of survivors or liberators. The passage of time has taken its toll and the numbers have shrunk dramatically. I miss greatly the survivors whom I had the honor to work with for so many years and who are no longer with us — far too many to name. They taught and inspired me greatly.

The reality is that with the passage of time and the loss of so many of our eyewitnesses, memory of the Holocaust is fading. And as that memory fades, so too does the world’s sense of responsibility to be vigilant against anti-Semitic attitudes and behavior. The postwar taboo that moved public espousal of anti-Semitism toward the margins is rapidly eroding; as a result, we have seen a surge of violent anti-Semitic attacks throughout Western Europe.

Add to that phenomenon the reality that growing obsessive animus against Israel provides camouflage for anti-Semitic attitudes, because such views are not seen as unbridled hatred of Jews — even when Jews are the target — but rather legitimate attacks on a nation state. The result is a toxic mix: the erosion of the taboo against publicly expressed anti-Semitism coupled with obscene attacks on Israel’s legitimacy that are given a pass.

A third ingredient that adds toxicity in Europe is the vilification of Israel in terms that suggest Israeli behavior is no better than that of the Nazis, that Gaza is Warsaw, and that Israel is committing genocide — outrageous lies that damage Israel’s standing and ominously provide Europeans with the excuse to assuage any sense of guilt over the Holocaust.

And finally, there is the frightening growth of anti-Semitism in segments of the Muslim community, which is filling a void left when Christianity distanced itself from anti-Semitism 50 years ago with the declaration of nostra aetate — repudiating the idea that Jews were responsible for killing Jesus.

Karen Armstrong, to my knowledge, does not hate Jews nor in any way endorse acts of anti-Semitism. Yet her profoundly offensive perspective is precisely the kind of warning sign to which we should pay attention. The increased willingness to tolerate anti-Semitism — because of the combination of fading memory, pathological antagonism toward Israel and the relief such vilification provides from guilt over the Holocaust, as well as a disinclination to confront anti-Semitism within segments of the Muslim community — is alarming.

Our ability to meet the challenge, and assist our brothers and sisters who feel increasingly vulnerable in European Jewish communities, rests on our understanding the intersection of these trends, which in turn will increase our understanding of how to dilute the toxicity of the mix. This should include increased attention to history lessons from the Holocaust and other examples of genocide about how to avoid becoming a bystander and how bystanders of evil come to regret their inaction. It should include challenging the left to open its eyes to the crossover from virulent anti-Israelism to anti-Semitism. And it should include more — not less — engagement with moderate voices in the Muslim community, as both our communities have a stake in how these profoundly important challenges are addressed.

Rabbi Doug Kahn is the executive director of the S.F.–based Jewish Community Relations Council.