I HAVE been wondering recently about how the idea of heresy got started, and why. It is a peculiar idea - the notion that certain beliefs are not merely false, but wicked, and ought to be suppressed - especially since the beliefs in question concern metaphysical issues, which have no practical import.

Why should it matter whether a person believes that the Father and the Son are of the same substance, or of similar substance; or, more fundamentally, whether the language of "substance" is legitimate - the business of the Council of Nicaea, and subsequent disputes about the doctrine of the Trinity?

Until recently, however, most Christians were convinced that theological correctness was of the greatest importance - not only for individual believers, but for the body politic. In some places, the presence of pagans, Jews, and heretics was commonly believed to cause earthquakes and other natural disasters; so Christian rulers, concerned for the well-being of their people, thought it incumbent on them to root out heterodoxy.

We still have not shaken off the idea that bad theology has bad, real-world consequences. Hardly anyone now imagines that heterodoxy causes natural disasters. But there are still people who are convinced that bad theology, or no theology, causes social ills, such as crime, violence, and disorder. This is the perennial theme of the Religious Right.

They are, of course, wrong. There is no more empirical evidence linking theological incorrectness to bad behaviour and social disorder than there is to assume that it causes hurricanes or tsunamis. Some of the most religious nations on earth - those in sub-Saharan Africa, with the largest bodies of committed Christians - are among the most violent and corrupt. Scandinavian countries, where religious belief is virtually extinct, are among the most orderly, least violent, and least corrupt places on earth.

This is not to say, pace the late Christopher Hitchens, that "religion poisons everything," but, rather, that it makes no difference.

These days, where I live, Christianity is not socially acceptable: admit to it, and you get, at best, the incredulous stare. Here there are, of course, the perennial village atheists, with their choice remarks about the Flying Spaghetti Monster, orbiting teapots, and a pitch that is not significantly different from the standard rhetoric popularised by Mencken and Sinclair Lewis almost a century ago.

But these days there are also the spiritual-but-not-religious, and their Neo-Pagan and faux-Buddhist kin. Unlike the crusading atheists, they are not against soft-headedness or sentimentality, and are not dogmatically dismissive of supernaturalism. They are just opposed to "organised religion", and, in particular, to institutional Christianity, which they understand as little more than a system of arbitrary rules for belief and behaviour, enforced by heresy-hunting Church functionaries.

They are wrong. Heresy-hunting has gone the way of chainmail and Middle English. It is not done, either by the state or by churches, which do not check credentials at the door, and could not, even if they wished, persecute heretics.

Metaphysics, which includes philosophical theology, has no practical import: religion is essentially inconsequential. Now that we recognise that, theology can become what it was before it became entangled with practical concerns: a philosophy, a speculative enterprise, and a source of wisdom and pleasure.

Dr Harriet Baber is Professor of Philosophy at the University of San Diego, USA.