It's comforting, perhaps, to dismiss Anders Behring Breivik as nothing more than a psychotic loner. That was the view of the Conservative London mayor, Boris Johnson, among others. The Norwegian mass killer's own lawyer has branded him "insane". It has the advantage of meaning no wider conclusions need to be drawn about the social context of the atrocity.

Had he been a Muslim, as much of the western media concluded he was immediately after the terrorist bloodbath, we can be sure there would have been no such judgments – even though some jihadist attacks have undoubtedly been carried out by individuals operating alone.

In fact, however deranged the bombing and shooting might seem, studies of those identified as terrorists have shown they rarely have mental illness or psychiatric abnormalities. Maybe Breivik will turn out to be an exception. But whether his claim that there are other members of a fascistic Christian terror network still at large turns out to be genuine or not, he has clearly fostered enthusiastic links with violent far-right groups abroad, and in Britain in particular.

Those include multiple contacts with the Islamophobic English Defence League, which has repeatedly staged violent protests against Muslim communities. "You're a blessing to all in Europe," Breivik apparently told EDL supporters in an online message, hailing "our common struggle against the Islamofascists". Whatever Breivik has done, he hasn't done in isolation.

Of course the Norwegian killer's ideology, spelled out in mind-numbing detail in his 1,500-page online manifesto, is both repulsive and absurd. Its main focus is hatred of Islam and Muslims — who he wants deported from Europe — rooted in a self-proclaimed Christian conservatism. He declares himself hostile to "cultural Marxism", while being both pro-Israel and antisemitic, and a champion of anti-Muslim rage from India to the Arctic circle.

The killer has evidently absorbed the far right's shift from the language of race to the language of culture. But what is most striking is how closely he mirrors the ideas and fixations of transatlantic conservatives that for a decade have been the meat and drink of champions of the war on terror and the claim that Islam and Islamism pose a mortal threat to western civilisation.

It's all there: the supposed Islamisation of Europe, the classic conspiracism of the "Eurabia" takeover fantasy, the racist hysteria about the Muslim birthrate, the inevitable clash of civilisations, the hatred of "multiculturalism" and the supposed appeasement of Islam by the European elite, which is meant to have fostered a climate where it's impossible to speak about immigration.

All these themes are of course staples of conservative newspapers, commentators and websites. So naturally, exponents of one or more of these tropes are quoted liberally by Breivik, from Bernard Lewis and Melanie Phillips to Ayaan Hirsi Ali and Mark Steyn.

Phillips, a Daily Mail writer, has complained of a "smear". But an article of hers Breivik cites at length described the former Labour government as guilty of "unalloyed treachery" for using mass immigration to "destroy what it means to be culturally British and to put another 'multicultural' identity in its place" – Breivik's feeling precisely.

None of these writers is of course in any way sympathetic to the carnage carried out in Norway last week. But the continuum between the poisonous nonsense commonplace in the mainstream media in recent years, the street slogans of groups like the EDL and Breivik's outpourings is unmistakable.

The same phenomenon can be seen across European politics, where the rise of rightwing Islamophobic parties from France and the Netherlands to Norway and Switzerland has encouraged the centre-right establishment to play the Islam card, wrap itself in "Christian" values and declare the chimera of multiculturalism an abject failure.

It's hardly surprising that some on the parliamentary right have recognised Breivik's ideas as their own: the Italian Northern League MEP Mario Borghezio described them as "100% good". But the same neoconservative zealots who have always insisted that non-violent (Muslim) "extremists" must be cast out because they legitimised and provided a "conveyor belt to terrorism" have now been hoist by their own petard.

That is exactly the role many of their own ideologists have been shown to have played in the case of the butcher of Utoya. When David Cameron denounced multiculturalism in February, he also announced – to the delight of the EDL – that the British government would now be taking on the "non-violent extremists" because they influenced those who embraced violence.

Don't expect the Islamophobic conspiracists to get the same treatment. Breivik is an isolated case, it will be said. In reality, as Europol figures demonstrate, the overwhelming majority of terror attacks in Europe in recent years have been carried out by non-Muslims. In Britain, a string of recent convictions of would-be anti-Muslim terrorists has underlined that Breivik is very far from being just a Norwegian phenomenon.

Lower-level violence and intimidation continues unabated: last week on the day of the Norwegian massacre, in an entirely routine incident, a mosque in Luton was vandalised and spray-painted with a swastika and EDL slogan. The rise of Islamophobia in Europe and the US is the manipulated product of a toxic blend of economic insecurity, unprotected mass migration and the consequences of a decade of western-sponsored war in the Muslim world: from Afghanistan to Iraq, Pakistan to Libya.

It has become the new acceptable form of racism – far outstripping in opinion polls the level of hatred for any other religious or racial group, and embraced by those who delude themselves that anti-Muslim bigotry has nothing to do with ethnicity – and even represents some sort of defence of liberal values.

For those who failed to deliver decent jobs, wages and housing, and encouraged employers to profit from low-wage migrant labour, how much easier to scapegoat minority Muslim communities than deal with the banks and corporate free-for-all that triggered the crisis? The attempt to pathologise last Friday's slaughter and separate it from the swamp that spawned it can only ratchet up the danger to all of us.