Can you imagine anything "so important that it must not be subjected to the risks of disconfirmation or serious criticism"? Intellectually, most of us would say not. But, in fact, we often act as though the answer is yes.

Take, for instance, certain ideas about equality. Many confuse the moral claim that all human beings should be equally valued and have the same rights regardless of ethnicity, with the factual claim that all ethnic groups have the same basic abilities. If this factual claim (which is probably true) is even tested, let alone put in doubt, they start shouting "racism". The belief is too important to even scrutinise.

Even science, which is all about testing and criticism, can be thought to be so important that certain beliefs about its scope and power should not be questioned.

This is the kind of cognitive prophylactic that Daniel Dennett had in mind when he talked, in Breaking the Spell, about "belief in belief". This occurs when a tenet comes to be seen, in his words, as "so important that it must not be subjected to the risks of disconfirmation or serious criticism". He thought that such a protective cloak should not be thrown over any belief, whether true or false, or whether that belief is in the empirical equality of human beings, the power of science, or of belief in God.

Such belief in belief, however, can come in at least three varieties. First, there is the social version, which holds that, whatever doubts the powerful cognoscenti may have, it is important that they foster belief in religious belief, or all hell will break loose. This view is often accused of being elitist (which it is) and patronising (which it may not be). To treat someone as though they were less intelligent than they are is patronising; to treat someone as though they were less intelligent than you, when they are indeed less intelligent than you, is not. That is why we do not patronise small children when we talk at their level.

I'm not convinced this kind of paternalism is good or necessary. Ethics aside, even on a pragmatic level, it both overestimates the power of elites to determine what the masses think, and the intellectual superiority of the ruling classes.

Second, and a more interesting possibility, is that we might justify belief in belief for ourselves. For instance, I remember talking to a trade unionist who sincerely believed that the world would be better without money, and that human beings are fundamentally good enough to thrive in such utopian conditions. When pushed on this, she said: "I have to believe that." Such examples of acknowledged belief in belief are not uncommon, although most people feel uncomfortable admitting to it.

But such dogged loyalty is surely only justified in extremis. If you are stuck on a mountaintop, the belief that you will get down if you try hard enough is too important to seriously doubt. In contrast, the belief that you will survive no matter what you do, is too dangerous to go unchallenged. In normal circumstances, however, no belief should be immune to scrutiny. Even if it seems you would be happier if you didn't test some comfortable convictions, in the long run, such evasion is often destructive. You may be happier today if you do not question whether your marriage really is in good shape, but if it isn't, your refusal to countenance the possibility is probably going to make things worse in the long run.

Belief in God is no exception, in the public and private cases. Despite the moral panics of traditionalists, there is no evidence that when religious belief deteriorates, society does too. Even if the questionable evidence that religious believers are happier and healthier than non-believers holds up, belief in truth shouldn't rest on instrumental benefits. It would take a very shallow Christian, for example, to switch faiths if she found that, on average, Jains lived longer, happier lives.

In some respects, the way I've framed the debate so far misses the point. Belief in belief is powerful precisely because it is not usually explicit. Rather, it is like a kind of in-built compass that directs away from the challenging and towards the confirming. Dealing with this is much more difficult than answering the somewhat tired question of whether it is right to promote religion as a "noble lie". (It isn't. Next.) Anyone who values truth, including atheists, has to strive very hard try to compensate for belief in belief's distorting effects. And that's no less the case when it appears in the guise of belief in unbelief.