Scientology is as worthy of belief as Christianity or Judaism. True or false?

I think I've got the dawkins; pray for me. It is a terrible condition, named after the distinguished atheist. This is not the ordinary cafard which descends like a cloud of ravening horseflies when I am trying to pay attention to an archbishop's thoughts. It is not even the sense of being stuck in a tumble drier half full of rocks that overwhelms me when I read papal encyclicals all the way through and try to follow their logic. It is worse than that. The full-blown dawkins is the state where there seems nothing to choose between any religion. They are all insane, all untrue - they might as well all be Aztecs.

The Aztecs make a wonderful subject for a student of religion since - nowadays - they have neither temples, priests, nor libel lawyers. They never had much use for libel lawyers anyway, preferring stone knives, with which they chopped out the hearts of anyone who displeased them. It was quite an elaborate ceremony and would not nowadays get past the animal rights people if you were nasty enough to perform it on a veal calf. Yet the Aztecs were undoubtedly sincere in believing that if they did not perform the ceremony every day, the sun would refuse to rise. And they undoubtedly had experiences that validated their beliefs. They were certain that God wanted them to do these things.

Is there any rational reason for supposing they were wrong? If one of my children announced that they were becoming an Aztec fundamentalist, how could I argue that I would prefer him to become a Buddhist, a Christian or Muslim instead?

When I have the dawkins, I believe that there is no rational argument to make; that religions are simply beliefs that people catch, and there can be no reasonable grounds to choose one over any other. This is not to say there are no reasons for seeing some religions as more desirable than others: there are rational, anthropological arguments to be made from the side effects, so to speak, of certain religious beliefs. The Hindu peasant who believes his bullock is sacred will not kill it however bad the famine, and thus may be able to plough when the drought finally ends, whereas his more rational neighbour, who ate the bullock, will starve in the end because he cannot plough. Thus do the gods reward those who follow them.

Even the Aztecs, as the anthropologist Marvin Harris pointed out, had a very ecologically sound religion. Central America in their time had no sources of animal protein larger than a guinea-pig; and though their god might get the prisoners' hearts, which were burned, the rest of the sacrificed carcass went to feed the soldiery. This protein bonus kept them motivated, as well as strong: the chief source of sacrifices was captured enemy prisoners, so any soldier on this diet will have known that surrender really was the option of the last resort.

However, the Aztec religion did not survive competition with Christianity. This is not just because flint weapons are no match for firearms. It was also because the Aztec church could not survive disestablishment. Without coercion, people found it unconvincing. So here is one clue as to how we might discriminate between religions: those that have lasted longest and in the most varied circumstances are likely to have something to recommend them, even if it is not immediately apparent what.

Religions do compete and do disappear. It is one of the oddest things about them. The disappearance is obvious: the Aztecs, the Romans, the Greeks, even the druids, have all gone. We do not really know what they believed, or how they believed it; only what they did. Almost everywhere that belief in many gods met belief in one god, monotheism triumphed. This pattern is odd. It suggests that religious beliefs do refer to some kind of metaphysical reality.

The monotheistic religions have also struggled with each other. All have developed rational arguments to keep the waverers within the fold, and to convert unbelievers. St Thomas Aquinas's great summary of the Christian religion was written as the Summa contra Gentiles: an argument against the Muslims. In fact all the great religions that we now see have been shaped by competition with others. All of them can give good reasons why the choice of religious belief can be made reasonably and is important. And yet, when one has the dawkins, all these reasons look ridiculous. The mere existence of interminable disputes seems to guarantee that there is something profoundly wrong about all the arguments.

This mood need last no longer than it takes to look at some real examples. Even within religions it is impossible to suspend judgement. An attitude of impartial and indiscriminate scorn cannot long survive contact with Ian Paisley or Morris Cerullo. Surely there must be Christians better than this. Compare the Dalai Lama with the staring-eyed cultists of some Western Buddhist sects, and there is no doubt which is the better Buddhist. I even have a soft spot for the late Ayatollah Khomeini, ever since I read his letter attempting to convert President Gorbachev to Islam. It was remarkably persuasive, lucid, and reasonably argued. Indeed, my own problem with Islamic fundamentalists is that they put too much faith in logic and expect the world to be more consistent than it actually is. Their arguments are by no means insane. If anything, the fault is that they lack the paradoxical quality which any explanation of the real world would seem to demand.

But it is almost always a mistake to judge any religion by the apparent sanity of the things it asks us to believe. Otherwise there would be no way of distinguishing between, say, orthodox Judaism and scientology.

The two are not yoked together entirely by chance. As the scientologists are pointing out every chance they get at the moment, both have been persecuted by Germans this century. But to make this claim involves a wilful blindness to the distinction between democratic and totalitarian governments. There is no evidence that the German authorities at the moment are behaving unjustly. None the less, there is clearly a considerable revulsion against scientology at all levels of German political life. The German post bank is refusing to handle deposits from the cult; various local authorities are refusing to allow contracts to go to businesses controlled by scientologists; the youth wing of the Christian Democratic Union organised demonstrations outside the film Mission:Impossible because its star, Tom Cruise, is a scientologist; the German minister of employment has announced that his country is at war with "the giant octopus of scientology".

The German foes of scientology are claiming that its beliefs are so absurd it cannot be a religion. The scientologists claim, with neutral academic backing, that they are a religion, so their beliefs cannot be absurd. Both are wrong.

To become a senior scientologist you have to believe, or pretend to believe, that we are all reincarnated alien spirits, persecuted by the ghosts of previous incarnations, which attach themselves to us in the form of body hairs. One can see why the organisation regards the psychiatric profession as a hostile conspiracy. On the other hand, to become Chief Rabbi one must believe, or pretend to believe, that Moses wrote the entire Pentateuch under dictation from God, including the bits where his own death is mentioned. We cannot distinguish between these two belief systems on the point of probability.

Longevity is a better bet. The Cambridge theologian Professor John Bowker refers to the great religions as "well-winnowed". This is a way of saying that they address unchanging human concerns and come up with answers that remain realistic.

A new religion tends to argue first that it is true, and second that its adherents prosper. A really confident sect will argue the second point first and loudest, as evangelical Christianity and scientology do now. But they only become trustworthy after they have abandoned the second point almost entirely.

Under the stress of time and chance and suffering, religions change, and sometimes quite radically. Sometimes this is because of conflicts within their own belief systems, where contradictions suddenly appear. Christianity accepted slavery for most of its history, and had good biblical reasons for doing so. When finally it became apparent to Christians - and it was overwhelmingly Christians who ended the slave trade - that the biblical defences of slavery could not be reconciled with other parts of the gospel message, then slavery went. A similar thing now is happening to Christianity and patriarchy, something which would have come as unwelcome news to the great majority of saints through the ages.

Orthodox Judaism, too, though it may reject historical criticism, has survived a much greater shock in its time; the final destruction of the Jerusalem Temple in AD70 and its replacement by scattered synagogues. Some such crisis is essential to the maturity of religions. Who can doubt that Judaism is better and richer now without the Temple - and that anyone who expects the Temple to be rebuilt, as prophesied, is probably looking forward to a nuclear war, since its remains are buried beneath the second holiest site in the Muslim world.

The dangers that bad religions can produce show that we must distinguish between good and bad religions. But how can we?

I think we must turn to a second sort of evidence, written in the lives of the believers. Religions all carry an ethical freight. They are injunctions to behave as well as to believe, and, in so far as the two can be disentangled, the behaviour is probably more important than the beliefs. But they cannot be very far disentangled. To a large extent the behaviour is the meaning of the belief. A Pharisaic injunction like "love your neighbour as yourself" cannot be properly understood without being acted on. The action shows you have understood it.

By contrast, the action that shows you believe and have understood doctrines of scientology is to hand over money to the heirs of L Ron Hubbard, the science fiction writer who made it all up. I think I can see which religion is more reasonable. The dawkins have quite gone away now, thank you.