Aside from the tragic loss of three innocent lives, the most notable element in the story of the Kansas Jewish Community Center shootings was what it told us about the nature of antisemitism. More specifically, what comments made by the perpetrator, Frazier Glenn Cross, a few years prior to the incident, told us. A long-time member of the Ku Klux Klan, he was of course involved in violence and other hate crimes against African-Americans, but when asked by irreverent radio personality Howard Stern which ethnic minority he hated more, his reply could not have been more unequivocal:

“Jews. A thousand times more. Compared to our Jewish problem, all other problems are mere distractions.”

There is something pathological about his antisemitism. And indeed about antisemitism in general.

The late, brilliant polemicist Christopher Hitchens (who discovered in middle-age that he was, in fact, Jewish) speaking in memory of the slain journalist Daniel Pearl, described antisemitism as “a mental illness” and “a plague”. Former Chief Rabbi of the UK, Jonathan Sacks has frequently spoken of it as a virus, mutating over time.

Hundreds of books and tens of thousands of articles have been written attempting to explain just how Germany, the cultural and intellectual capital of Europe, fell so easily and willingly into the arms of something so irredeemably evil as Nazism. To the specific question of why was Hitler’s antisemitism accepted, lived with, excused, or supported by so many ordinary Germans, a simple answer is that much of the country had already contracted this virus – it was latent in German society for decades – even if they did not have as virulent a strain as did their paranoid, power-mad Fuhrer.

Even in Britain, arguably the easiest place to be a Jew in western Europe in the period leading up to the Second World War, the sickness existed. It was summed up perfectly by the real-life character of Harold Abrahams in the movie Chariots Of Fire when he describes the subtle anti-Jewish prejudice that he regularly encountered: “You catch it on the edge of a remark.”

Hitler regarded Slavs, Poles and other eastern Europeans as untermenschen, inferior human types fit only as slaves for the Aryan master race. But it was Jews, and only Jews, who were simultaneously less-than-human and a diabolically brilliant foe manipulating the world.

The fascism of today, Jihadist Islam, hates Christians and Hindus and, indeed, many other Muslims, but it is the Jews alone who defied the Prophet Muhammad and now, some 1500 years, are pulling the levers of power in western capitals and dare to occupy Muslim land in Palestine.

As a pathology, antisemitism has never required intellectually coherent reasoned rationales. Jews were the purveyors of international communism, and the hidden puppet-masters orchestrating global capitalism. They were to be vilified as wandering, stateless “rootless cosmopolitans”, and are the only people whose sovereign state is inherently illegitimate.

And of course criticism of Israel is not inherently antisemitic, but when the democratic Jewish state is condemned as uniquely evil by people who turn a blind eye to the routine and brutal abuse of human rights in dozens of other countries, the age-old plague is the only plausible explanation.

“…one of the marks of antisemitism is an ability to believe stories that could not possibly be true” wrote George Orwell in a fine essay on the subject.

Unfortunately today – as ten years ago, a hundred years ago and a thousand years ago – millions of people are driven to hatred of Jews by the myths, and libels and conspiracy theories that feed the pathology. The Kansas City shooter Frazier Glenn Cross is part of a global network of white supremacists and neo-Nazis, and there should no whitewashing the demagogic far-right parties ominously making political gains in Hungary, Greece and elsewhere in Europe.

On a much larger scale, and of greater global significance, Islamists both Sunni and Shi’a have made antisemitism an absolute pillar of their worldview. Hamas, the Muslim Brotherhood in Egypt, the Iranian proxy Hezbollah – all indulge in routine citation of Quranic verses condemning Jews as the “descendants of pigs and monkeys”, all make use of classic European anti-Semitic tropes from the Blood Libel to ‘Protocols of the Elders of Zion’. Holocaust revisionism has often featured – most famously of course as official Iranian state policy.

And whatever one thinks about the use of Holocaust analogies by Israeli leaders, all of this does have a bearing on the here and now in the Middle East. In the wake of the latest Fatah-Hamas rapprochement, those expecting Israel to “give Hamas a chance” should be forced to read Hamas’s founding charter and see for themselves that it’s the most brazenly antisemitic political document since ‘Mein Kampf’. Far too often, particularly in the mainstream western media, the Arab-Israeli conflict is analyzed and described as purely a territorial conflict, overlooking completely the antisemitic subtext of much of the Arab rejection of any Jewish sovereign presence. The main instigator of anti-Jewish riots and pogroms in British Mandate Palestine was the Mufti of Palestine, Haj Ami al-Husseini, a fanatical anti-Semite who spent much of the Second World War as Hitler’s guest in Berlin, plotting to bring the Final Solution to Palestine.

Antisemitism is a plague. It is almost certainly ineradicable but that doesn’t mean it should not be fought at every turn. History teaches that an antisemitic society is a sick society; and that regimes or political parties infected with Jew-hatred deal in the currencies of mass violence and barbarism. Appeasement of such an evil – whether it comes from the secular far-right, or from the forces of Islamism – will end in disaster, and not just for the Jews.