That is precisely what a modern "smart missile" can do. Computer miniaturisation has advanced to the point where one of today's smart missiles could be programmed with an image of the Manhattan skyline together with instructions to home in on the north tower of the World Trade Centre. Smart missiles of this sophistication are possessed by the United States, as we learned in the Gulf war, but they are economically beyond ordinary terrorists and scientifically beyond theocratic governments. Might there be a cheaper and easier alternative?

In the second world war, before electronics became cheap and miniature, the psychologist BF Skinner did some research on pigeon-guided missiles. The pigeon was to sit in a tiny cockpit, having previously been trained to peck keys in such a way as to keep a designated target in the centre of a screen. In the missile, the target would be for real.

The principle worked, although it was never put into practice by the US authorities. Even factoring in the costs of training them, pigeons are cheaper and lighter than computers of comparable effectiveness. Their feats in Skinner's boxes suggest that a pigeon, after a regimen of training with colour slides, really could guide a missile to a distinctive landmark at the southern end of Manhattan island. The pigeon has no idea that it is guiding a missile. It just keeps on pecking at those two tall rectangles on the screen, from time to time a food reward drops out of the dispenser, and this goes on until... oblivion.

Pigeons may be cheap and disposable as on-board guidance systems, but there's no escaping the cost of the missile itself. And no such missile large enough to do much damage could penetrate US air space without being intercepted. What is needed is a missile that is not recognised for what it is until too late. Something like a large civilian airliner, carrying the innocuous markings of a well-known carrier and a great deal of fuel. That's the easy part. But how do you smuggle on board the necessary guidance system? You can hardly expect the pilots to surrender the left-hand seat to a pigeon or a computer.

How about using humans as on-board guidance systems, instead of pigeons? Humans are at least as numerous as pigeons, their brains are not significantly costlier than pigeon brains, and for many tasks they are actually superior. Humans have a proven track record in taking over planes by the use of threats, which work because the legitimate pilots value their own lives and those of their passengers.

The natural assumption that the hijacker ultimately values his own life too, and will act rationally to preserve it, leads air crews and ground staff to make calculated decisions that would not work with guidance modules lacking a sense of self-preservation. If your plane is being hijacked by an armed man who, though prepared to take risks, presumably wants to go on living, there is room for bargaining. A rational pilot complies with the hijacker's wishes, gets the plane down on the ground, has hot food sent in for the passengers and leaves the negotiations to people trained to negotiate.

The problem with the human guidance system is precisely this. Unlike the pigeon version, it knows that a successful mission culminates in its own destruction. Could we develop a biological guidance system with the compliance and dispensability of a pigeon but with a man's resourcefulness and ability to infiltrate plausibly? What we need, in a nutshell, is a human who doesn't mind being blown up. He'd make the perfect on-board guidance system. But suicide enthusiasts are hard to find. Even terminal cancer patients might lose their nerve when the crash was actually looming.

Could we get some otherwise normal humans and somehow persuade them that they are not going to die as a consequence of flying a plane smack into a skyscraper? If only! Nobody is that stupid, but how about this - it's a long shot, but it just might work. Given that they are certainly going to die, couldn't we sucker them into believing that they are going to come to life again afterwards? Don't be daft! No, listen, it might work. Offer them a fast track to a Great Oasis in the Sky, cooled by everlasting fountains. Harps and wings wouldn't appeal to the sort of young men we need, so tell them there's a special martyr's reward of 72 virgin brides, guaranteed eager and exclusive.

Would they fall for it? Yes, testosterone-sodden young men too unattractive to get a woman in this world might be desperate enough to go for 72 private virgins in the next.

It's a tall story, but worth a try. You'd have to get them young, though. Feed them a complete and self-consistent background mythology to make the big lie sound plausible when it comes. Give them a holy book and make them learn it by heart. Do you know, I really think it might work. As luck would have it, we have just the thing to hand: a ready-made system of mind-control which has been honed over centuries, handed down through generations. Millions of people have been brought up in it. It is called religion and, for reasons which one day we may understand, most people fall for it (nowhere more so than America itself, though the irony passes unnoticed). Now all we need is to round up a few of these faith-heads and give them flying lessons.

Facetious? Trivialising an unspeakable evil? That is the exact opposite of my intention, which is deadly serious and prompted by deep grief and fierce anger. I am trying to call attention to the elephant in the room that everybody is too polite - or too devout - to notice: religion, and specifically the devaluing effect that religion has on human life. I don't mean devaluing the life of others (though it can do that too), but devaluing one's own life. Religion teaches the dangerous nonsense that death is not the end.

If death is final, a rational agent can be expected to value his life highly and be reluctant to risk it. This makes the world a safer place, just as a plane is safer if its hijacker wants to survive. At the other extreme, if a significant number of people convince themselves, or are convinced by their priests, that a martyr's death is equivalent to pressing the hyperspace button and zooming through a wormhole to another universe, it can make the world a very dangerous place. Especially if they also believe that that other universe is a paradisical escape from the tribulations of the real world. Top it off with sincerely believed, if ludicrous and degrading to women, sexual promises, and is it any wonder that naive and frustrated young men are clamouring to be selected for suicide missions?

There is no doubt that the afterlife-obsessed suicidal brain really is a weapon of immense power and danger. It is comparable to a smart missile, and its guidance system is in many respects superior to the most sophisticated electronic brain that money can buy. Yet to a cynical government, organisation, or priesthood, it is very very cheap.

Our leaders have described the recent atrocity with the customary cliche: mindless cowardice. "Mindless" may be a suitable word for the vandalising of a telephone box. It is not helpful for understanding what hit New York on September 11. Those people were not mindless and they were certainly not cowards. On the contrary, they had sufficiently effective minds braced with an insane courage, and it would pay us mightily to understand where that courage came from.

It came from religion. Religion is also, of course, the underlying source of the divisiveness in the Middle East which motivated the use of this deadly weapon in the first place. But that is another story and not my concern here. My concern here is with the weapon itself. To fill a world with religion, or religions of the Abrahamic kind, is like littering the streets with loaded guns. Do not be surprised if they are used.

Richard Dawkins is professor of the public understanding of science, University of Oxford, and author of The Selfish Gene, The Blind Watchmaker, and Unweaving the Rainbow.