Howard Jacobson: A little religion, laced with compromise, goes a long way. Only madmen live by purity

Once belief hardens into dogma, the believer enters the terrain of derangement

The letter killeth. I can see why there is urgency within the Muslim community to disown terrorism as a perversion of Islam as strictly understood. But therein lies a contradiction. For it is not difficult to show that adherence to the strictness of Islam, as indeed to the strictness of any religion, is the first step on a ladder which will take some to sanctity, but just as many, in the name of sanctity, to violence.

Onward march the Christian soldiers, despite Christ's refusal of militarism. Though the Bible teaches Jews to love the stranger, there are some Jews who find justification in the Bible not only for despising strangers but for making strangers of them where they live. And in the name of Islam, such crimes have been committed as would make the angels weep.

Never mind that this is not what any of the great faiths have meant to teach. Belief itself is where the problem starts. Laced with the usual humanising laxities and compromises, belief can be an innocent affair. And a little of it, in a naughty world, can go a long way and do a fair amount of good. But once belief hardens into a dogma which allows no deviation - call it orthodoxy or call it fundamentalism - the believer enters the terrain of derangement. Purity has its attractions, but only madmen live by it. "Objection, evasion, cheerful mistrust, delight in mockery are signs of health," said Nietzsche. "Everything unconditional belongs to pathology."

Freud intended a service to the Jewish people when he argued that Moses was an Egyptian. In one stroke he reminded us that neither our most significant prophet, nor the Judaism he taught, was pure. This is not against the spirit of what the Old Testament itself says of Moses - concealed in an ark of bullrushes daubed with slime and found by Pharaoh's daughter who brings him up lovingly as her own. A little bit of somewhere else, we are to understand, a little daubing with impurity, was necessary to make Moses who he was.

The requisite genealogy, this, for all the great men of mythology who give their names to new civilisations or beliefs. They are abandoned to shepherds, they are raised by wolves, they are discovered by alien princesses with compassion in their hearts. It is as though the founding hero, in order to be worthy to lead his people, must first be mongrelised. Thus does the mythical history of mankind give the lie to all theories of national greatness based on racial homogeneity, and to all religions insisting theirs is the one and only truth.

Everything unconditional belongs to pathology. But we would be fools to suppose that the only pathology into which our home-grown terrorists were initiated was that of the mosque. Where were they educated into this, we beat our breasts and ask. From whom did ordinary and apparently amicable Muslim boys from Yorkshire acquire this ideology of hate?

Forgive the brutality of the answer. From us! No doubt it took an induction into unconditional theology to ignite them ultimately into violence. And no doubt men more experienced in the ways of terror primed their final resolution. But what we call their disaffection - that miasma of rage and bewilderment and misinformation without which this death cult could never have taken hold of them - is the staple diet of our own left-leaning news media, no more virulent than anything the educated middle classes have been expressing for years, the received wisdom of teachers, students and academics from one end of the country to the other.

Iraq, Afghanistan, Israel, Kashmir, the Balkans - you name them - all proof of the corrupt Western world's greed, degeneracy and Islamophobia. No sooner did the bombs detonate than we were chanting the litany of our sins again. We had it coming. On the letter pages of every newspaper, the same. Our fault. Our fault. And if we think it is our fault, why shouldn't they?

Basic laws of human decency, Law One: you do not say we had it coming when it is someone else who dies. If you want to say we had it coming, say it when "you" die. You can accept guilt for yourself; you cannot accept it for another person.

Decency aside, the we-had-it-coming lobby are those who, like the pure religionists of hate, subscribe to a purist interpretation of events. It should be no surprise to us to learn that the suicide bombers were not from among the unlettered poor. These days we must worry a) when our children fall quiet and take to reading holy scripture, and b) when they go to university. Neither can now be recommended to the impressionable. Both inculcate the unconditional.

Witness the historical illiteracy of those academics who nearly pulled off a boycott of Israeli universities a few months ago - determined to see only one side of a cruelly complex conflict - and remember those marches which academics and their charges could not wait to join, associating one cause about which there is to be no discussion with another, and where the faithful have been so catechised into conformity that to demur from a single atom of the rationale would be apostasy.

Afghanistan and Iraq are comparable only if you think every move the West makes is ipso facto Satanical. And even the invasion of Iraq, however impetuous, brutal and misguided, was not inspired by wanton wickedness alone. As for Zionism, that mantra of universal loathing, it is an aspiration to a homeland, not an ideology of hatred directed at Muslims. And if it doesn't look that way to Muslims, that's all the more reason why it shouldn't be depicted irresponsibly by us.

We don't help Muslims by flattering them in their conviction of oppression. Muslim paranoia, about which as a Jew I must admit I know something, is not only brewed up on Muslim streets. We feed it with the theology of our self-disgust. Unconditional in our hatred of our own culture, we strengthen unconditionality in others. And when that many pathologies collide, it's no wonder there's a bang.