Something is amiss when you cannot give a name to the evil you oppose

Lest he be misunderstood, the major general went on: "We have not defeated the idea. We do not even understand the idea." Rarely has the old injunction to "know thine enemy" been trashed so thoroughly.

By January of this year, according to the Pentagon, the US and its allies had hit 3,220 IS targets in Iraq and Syria. The figure will have increased greatly since, day upon day. Yet many observers regard even that effort as a barely adequate response to a barbaric, existential threat. Still you pause. Something is amiss when you cannot give a name to the evil you oppose.

Something worse is wrong if you flock to offer your life to a reviled cause you do not understand or, still worse, wish to understand. If the major general cannot define his foe's ideology, what did the three Dawood sisters from Bradford truly know when, it is assumed, they took nine children into the Syrian war zone to join a brother fighting for IS?

Language is being worn out. When a 17-year-old from Dewsbury, Talha Asmal, earns the indecent honour of becoming "Britain's youngest suicide bomber", all the useless words are lined up, ready for deployment: "radicalisation", "grooming", "propaganda", "alienation", "faith", "values", "jihad", "loyalties". None touches the paradox.

On the one hand, it is not credible to argue that the boy or the three sisters could expound the year-zero caliphate "ideology" of IS coherently. The insurgents themselves have yet to manage that feat. On the other hand, the young Muslims - almost always young - who set off for Iraq or Syria cannot claim to have been deceived.

The beheadings, the tortures, the sexual slavery, the cultural nihilism, the ethnic and religious massacres: these are not news. If you can manage to dismiss it all as crusader propaganda - a giant leap into fantasy, given jihadi videos and boasts - you must still contend with the judgement of every mosque in the land. IS is an insult to Islam. Nothing in the Koran justifies its acts or its "teachings".

A few facts don't hurt. As of the 2011 census there were 2,786,635 people in Britain identifying themselves as Muslim. According to the Foreign Office, around 500 have travelled to Iraq and Syria to join IS. Khalid Mahmood, Labour MP for Birmingham Perry Bar, thinks 2,000 is a "better estimate" of what he calls "a huge, huge problem". But even 2,000 is a vanishing fraction (not quite 0.075%) of a community whose revulsion at IS is deeper than anything experienced by a safe and secure government minister.

Still, 2,000 is not trivial given what is at stake for individuals, what it says about the IS threat, and what it says about Britain. You could dismiss a Thomas Evans, converting to become Abdul Hakim and die fighting for al-Shabab in Kenya, as a disturbed young man deceived by terrorists. Most reports say you would be right. But, as with all the others, 500 or 2,000, you would need to explain why his moorings in British life and society were so fragile to begin with.

To mistake al-Shabab or IS for noble causes requires absolute ignorance, extreme gullibility, or matchless stupidity. Equally, those cults hold sway, like sects from all religions, over those who respond to power, who desire submissiveness. IS deals in absolutes and finalities. It tolerates no dissent, allows no debate. Some yearn for that. If it leads them, by inverted logic, to the point of believing that slaughter justifies slaughter, argument is beside the point. Then we are all as baffled as Major General Nagata.

Against this reality, we have the likes of David Cameron talking about what he calls British values. This column has made the joke more than once: sit me down for one those citizenship tests and I would probably fail. But when the Prime Minister speaks of what matters there is no serious dispute: tolerance, fair play, free speech, the rule of law, respect for all faiths and none. You could point out that those values are also American, or Norwegian, or Irish. Given the alternatives, they'll do. On Friday, while describing IS as "one of the biggest threats the world has ever faced", the PM at least acknowledged the challenge of "making sure young people in our country feel truly part of it".

Groomed or not, foolish or not, those who join IS make a choice. One choice is to reject everything on the Cameron list. All sects, of all religions, have the habit. Given an argument between the truth revealed by faith and the compromises of the western Enlightenment, the instincts of an American creationist and a jihadi don't differ much. The important difference - the difference we will not tolerate - is mass murder.

That is, of course, the tepid white liberal argument. Things look different to many of those 2.78 million Muslims who endure the racism masked by talk of tolerance, who hear all those "debates" about immigration and know precisely what is meant, who understand that, often enough, the rhetoric of "British" has a precise meaning: not you.

It's one part of the story, but not even half of an explanation for IS recruits. It is easy enough to point out that the dream of a global caliphate founded on a mad misreading of the Koran leaves no room for anyone's version of tolerance. You can argue, fairly, that persistent Western failures to aid suffering Muslims, from Bosnia to Syria, could make any young idealist cynical. But what does IS chiefly do? It recruits Muslims to kill Muslims. That's the largest crime.

Alienation from Western society, its decadence, hypocrisy and racism, is one thing. To be seduced by the glamour of firepower, if you identify with the downtrodden, is another. To set yourself against the Assad dictatorship or any other lousy regime might even seem honourable. IS exploits all of that. But the killing of Muslims is its stock in trade.

Others, better equipped than this writer, can make those arguments. What's clear is that glib talk of radicalisation doesn't explain what's going on among Muslim communities around Europe. Even the utopianism of IS, if that's your taste, has surely been exposed by now, yet the flow of recruits continues. For the handful, for the convinced minority, Britain and its values are no sort of alternative. And if 2,000 is a good estimate of a handful, how should we count those who accept the arguments, if not the deeds?

Too many in the West have given up arguing. IS, the enemy they can't quite define, counts as a kind of perverse exoneration for their Iraq catastrophe. Every barbaric attack justifies everything they ever said about Islamism and terror. That won't do. There are 2.78 million Britons who see children running off to wage war on command, against their own country and every other.

IS is not in the business of debate. Education will not solve this when murderers boast of their hellish deeds. Insisting on those British values is fine and well, for the majority. Causing the minority to understand that values are truly common to all is the hard, unfinished task.