Do not be under any illusion. The attacks against Muslims in New Zealand cannot be swept under the carpet by claiming that the suspect is an isolated actor or a disturbed individual. From what I have seen, the threat is far more serious than that – and the responsibility for facing up to it falls on all of us. The kind of Islamophobia that appears to have driven these killings goes far beyond some radicalised individual. It’s a thread that runs throughout the west – and we must confront it, now.

The temptation is going to be to declare the suspect, who livestreamed himself on Facebook shooting dozens of Muslims while they gathered for Friday prayer, a madman. It would be comforting to think so. Because then we could put aside any recognition that the discourse he appears to have bought into, evident from the manifesto he posted a link to on his now-deleted Twitter account, goes far beyond simply him.

But that would be a mistake. The themes of that manifesto – that Muslims are invaders, intent on replacing the white majority in Europe and the west – are indelibly linked to others on the far right, such as Anders Breivik, who went on his own murderous rampage in 2011 in Norway. But it has a long pedigree in western societies and is not restricted to the political fringes.

After the 7 July bombings happened in London in 2005, I was appointed as deputy convenor of a UK government working group on radicalisation to look at precisely which factors led to people becoming swept up in extremism. We examined the role of ideas and ideology, and concluded that they played a significant part – that we could not simply cast aside the importance of extremist discourse and dogma. There were, and are, other factors: political dissent, exclusion, and so on – but it would be wrong to minimise the extent to which ideas energised people, and provided their rationalisation for violent acts.

By the same token, it would be outrageous to fail to recognise that the unbridled, nativistic, anti-Muslim bigotry that has become so widespread in our societies has nothing to do with this attack in New Zealand. New Zealand is a part of the west. And, as far as the manifesto is concerned, the west writ large is subject to a Muslim invasion. That sentiment is not limited to a far-right extremist with a gun in a mosque, killing Muslim worshippers. It is popularised by scores of people in far more mainstream arenas.

Jacinda Ardern says Christchurch mosque shootings were terrorist attack – video

Every time some far-right populist promotes the idea that Muslims are a threat to our civilisation, this feeds into a climate in which the views espoused by the manifesto are seen as less extreme. And every time we deny the threat of anti-Muslim bigotry, or underestimate the extent of Islamophobia – including in our party of government, the Conservative party – we give succour to those in our society who seek to whip up hate against our Muslim communities.

Today is Friday. It is the day of the week when Muslims will gather all around the world in communitarian prayer. Many of them in the west will be fearful after seeing the news, worried that this attack may herald a new, ongoing threat to their safety. We have to make sure they know they are not alone. That wider society will stand by them. That we see them not as Muslim communities transplanted into the west, but as Muslim communities of the west. They are part of us, and we of them. If we do otherwise, and we allow this event to pass us by without recognising the ideas that propelled it, then it is only a matter of time before it is repeated.

• HA Hellyer is a senior associate fellow at the Royal United Services Institute and the Atlantic Council, and the author of Muslims of Europe: the ‘Other’ Europeans