I live in terror of the fanatic who has only read one story, whether he’s an Islamist murderer or Glenn Greenwald

So how fare our investigations into what makes someone want to kill cartoonists? (I’m assuming we know why they want to kill Jews.) Maybe, before pondering the education of a jihadist, we should ask a prior question: what makes a fanatic?

We were given some insight into this on Newsnight earlier this week when Evan Davis, growing nicely into his job, interviewed the lawyer, journalist and associate of Edward Snowden, Glenn Greenwald – a man strikingly deficient in the musculature necessary to essay a smile. The subject was surveillance and David Cameron’s call for more of it. There are, I accept, differing views on this. I, for example, am for having every member of the human family watched day and night by every possible means because the human family is currently dysfunctional and can’t be trusted. But I understand why others don’t think as I do. This puts me in a different category of person from Greenwald, who allows no beliefs that conflict with his and attributes those that do to a cowardly subservience to authority.

Leading Greenwald with expert gentleness into the gated hell that is his mind, Davis put the case for differing viewpoints. Nothing could have been more instructive than Greenwald’s dead expression – his mouth fixed in the rigor mortis of absolute conviction, his eyes unanimated by the pleasure of conversation or the excitement of controversy. Doubt honours a man, but this was the face of someone whom no ghost of a second thought dares visit. No consciousness of absurdity either. As for the humanity whose civil rights he champions with such icy rigidity, for that he had nothing but contempt. We are merely, if we don’t think what he thinks, the playthings of the powerful. This is the terrifying paradox of zealotry: no one hates humanity more than those who believe they know what’s best for it.

I don’t, I must say, see Greenwald launching rockets any time soon. The ideologue is still a long way from being the terrorist. These, though, are the first steps. Expelling doubt. Refusing contrariety. Hating play. Making oneself the human equivalent of a weapon, implacable, well aimed, reduced to a single function.

Another way of putting this is to say that the fanatic is someone who has only ever read one book. It is right, therefore, to ask not only what the appeal of the story he goes on reading is, but where he heard it, who read it to him first, and where and why it goes on being told. Religions, like cultures, understand themselves through narrative. How we came into the world, what we were created for, what are our triumphs and our losses. These narratives enjoy a fearful pertinacity. They have the capacity to console but also to inflame. There are still people fighting over territory declared holy by their national stories a millennium ago.

So it was heartening to see the French – offenders and offendees, or at least some of them – putting aside their individual stories for an hour. But the anti-immigration demonstrations in Germany were reminders that masses on the move are frightening as well as stirring. A group that has only ever read one book is a fanatic group.

For all the day-long defiance of terror, fear continues to stalk the conversation. Fear for Muslims, for example, and fear of them. May I make a plea, in the name of varied reading – because it’s better to read even two books than one – for the right to hold both positions. I don’t want to see anti-Muslim demonstrations on the streets. I no more want to see Muslims homogenised and traduced than Jews. But must that mean I cannot ask where the single story beloved of the fanatic is engendered, and if it should turn out that the most moderate Muslim unthinkingly propounds a narrative that fuels the fanatic mind – an anti-Western, anti-Semitic, victim-driven narrative – can I not plead with him to shade it a little, to remember that the best stories liberate us from our pains and grievances into understanding other people’s.

We rightly shy from holding communities to immediate and unambiguous account for what their most errant children do, but is it wise, is it honest – reader, does it make the world a better place for any of us – to raise the charge of Islamophobia the moment someone questions the communal atmosphere such errancy might have breathed? At the heart of every narrative of belief is a weak spot of exclusivism and dogma waiting to be exploited by its wilder adherents. Monotheism is a grand conceit, but can we really say that it is innocent of the millions of killings in its name? Danger lurks in the tales we all tell. And whoever goes on telling a tarnished tale is party to its effects.

“Nothing – absolutely zilch – happens without a past,” Robert Fisk wrote recently. But the past is not forever fixed; it too is a story, endlessly spun and woven, told and retold, now this way, now that. A Paris jihadist spoke of turning to terror after seeing Americans torturing Iraqi prisoners on television. It is not to defend such barbarities to say they were but one side of a savage conflict. They too had a past. They did not express the immutable will or character of the American people. A half-truth is a half-lie. The invasion of Iraq, however botched, had a past we falsify if we see it only as a story of Western skulduggery. It is a false tale, falsely told, that Israelis wantonly butcher children in Gaza. It is a false tale, falsely told, that the West is waging war against Islam. Whoever lusts after coherence lusts after lies.

The fanatic craves a single, simple story. Communities of whatever persuasion who provide the pen and paper, ink and plot, should search their hearts. But who are we to talk? We too, in our lurid self-censoriousness, tell madmen tales they love to hear.