The poison of antisemitism exists among a minority on the left; there is a wider group of people who deny it exists, or are even oblivious to what antisemitic tropes are, and refuse to educate themselves. There are also non-Jews who regard antisemitism as a useful tool, a convenient political device –and nothing else – to attack, undermine and demonise the Labour leadership and broader left. Both of these statements are inarguable, and both speak to the different political factions undermining the historic struggle to obliterate the disease of antisemitism.

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A minority of leftists seem to recognise only the most undiluted, violent antisemitism: as if somehow only a full-blown, Holocaust-denying neo-Nazi qualifies. While all Nazis are antisemites, most antisemites are not Nazis. Because antisemitism is at least two millennia old – the pogroms, expulsion, murder, blood libel, genocide – it permeates western culture and beyond. It has deeply embedded roots and manifests in subtle as well as overt forms. Some self-described leftists point out that, yes, some uncritical defenders of the Israeli occupation undeniably smear any solidarity with Palestine as antisemitic. But then they argue that all claims of antisemitism are simply pro-Israeli propaganda. To respond to claims of antisemitism in such a way is no better than those who complain, “You can’t say anything any more without being accused of racism.” Jewish socialists, including those who helped Jeremy Corbyn’s leadership campaign such as Jon Lansman – who has received vile antisemitic abuse from those purporting to be leftists – are genuinely fearful and insecure about antisemitism. Listen to the radical Jewish socialist organisation Jewdas , which has written detailed guidance about confronting leftwing antisemitism. It would be criminal for leftists to ignore their fears as overblown or the product of rightwing smears: would we not rightly listen to Muslims, or gay people, or women, talking about Islamophobia, homophobia or sexism?

This means properly understanding the classic antisemitic tropes. One is of sinister Jewish financiers exploiting the downtrodden: as Corbyn put it in a letter to Jewish leaders last week, this trope dates from the 19th century, and was termed the “socialism of fools” by the German left. Then there’s the trope of Jews wielding disproportionate power. While leftists understand capitalism as a system of power relations, conspiracists talk of shadowy figures and cabals running the world behind the scenes: you’ll often hear them ranting about the Rothschild family, rather than critiquing the financial system as a whole. This conspiracist perspective lends itself to antisemitism.

This is not using the bad behaviour of others to avoid confronting your own: the left must act, and will

The left has to get its own house in order for a number of reasons. “The Tories are worse” is not an excuse to avoid a reckoning. Our standards must be the highest, because our cause is the elimination of bigotry, exploitation and oppression in all their diverse forms. We exist to overturn the existing order, not to replicate and internalise its ugliest features. That is why Corbyn’s expressed militant opposition to antisemitism is so important, as is Momentum’s statement demanding the left confront it, as is the stated determination of Labour’s new general secretary, Jennie Formby, to defeat this bigotry. It means the left addressing our collective failings. Corbynism brought hundreds of thousands into politics for the first time, but in the absence of an existing mass socialist movement, many lacked political education. Rectifying that must surely be a priority for Formby and Momentum – as well as the full implementation of the Chakrabarti recommendations following her inquiry into the party in 2016.

But that does not mean we should take lessons from the political right. This is not “whataboutery”, which is using the bad behaviour of others to avoid confronting your own: the left must act, and will. But we’re not going to take lessons from a media that deployed antisemitic dog-whistles against Ed Miliband, including smearing his dad as “the man who hated Britain”, and harping on about how weird the “north London intellectual” looked. From a media that every day brims with filth and lies against Muslims, immigrants, refugees and gay and trans people – just as it once targeted Jewish refugees. Nor from rightwing websites whose comment sections are cesspits of racist, homophobic and antisemitic hatred. From a Tory party that used the EU referendum as an excuse to whip up bile against immigrants and refugees (with hate crimes surging as a result), whose members and councillors spray Islamophobic bile online. Or from Tory supporters who pollute the online sphere with racist abuse against one of Corbyn’s lifelong allies, Diane Abbott. The most rotten, racist and bigoted elements of British society – who not so long ago denounced the anti-racist left as the PC brigade who hated free speech – will not be allowed to rebrand themselves as paragons of moral virtue.

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As for those Labour elements – they know who they are – who believe antisemitism is a useful device to undermine the left: your net contribution is to undermine the struggle against antisemitism, nothing else. The left must accept that antisemitism does fester in certain quarters, and that some are in denial about that. And we all have to understand the continuing cost of not comprehensively defeating antisemitism in all of its manifestations.

Meanwhile, our failure to act leaves our Jewish sisters and brothers insecure, depressed and frightened. And it fatally undermines our historic mission, because we will not build a socialist society liberated from injustice if our movement is hampered by the bigotry we exist to extinguish. Take no instruction from the right – they have no standing in this matter. But until every last vestige of antisemitism is eradicated, we cannot flinch.

• Owen Jones is a Guardian columnist