Asda's apology: What on earth can have possessed it?

'Mental' costumes show how quickly we tend to dismiss the unfamiliar

Since Thursday, when first Asda then Tesco withdrew Halloween fancy dress costumes depicting mental health patients as deranged killers the furore has lost none of its spark. Alastair Campbell and Stan Collymore piled in. Jack Dee announced he's bought his Halloween costume – he's going as MD of Asda.

And yet – these fancy dress costumes wouldn't have been marketed if they didn't tap into something deep. Last week's pain and upset is just the latest episode in a nasty but little noted thread in history – the horror and repulsion which may be aroused by people whose thoughts, feelings and experiences we fear are different from our own and are, therefore, unpredictable. Where the difference is so extreme that people hear voices or see visions, for example, we become extremely uncomfortable. When early European settlers encountered a different form of consciousness in native peoples, the result was shameful.

History also shows that religion is often tied up with this horror of different types of consciousness, and this is true even in the case of the fancy dress fiasco. On the surface, Halloween is a chance for tacky retail promotions, but underneath it is an ancient religious festival.

The period from the autumn equinox to 2 November has traditionally been seen as a time when the membrane between the everyday world and the spirit world dissolves and spirits and demons walk the earth: the Celtic festival of Samhain, the Mexican Day of the Dead and, according to Robert Kirk, a pupil of Robert Boyle, who conducted a scientific survey of supernatural experiences in the Scottish Highlands at the end of the 17th century, a time when people would not go outdoors for fear of being attacked by tribes of "Subterraneans".

Boyle and Kirk were, like their contemporary Sir Isaac Newton, pioneers of a scientific revolution, and as scientific thought hardened into a materialism that left no room for God, angels and the spirits of the dead, many came to see the sorts of experiences that Kirk's highlanders described as delusions. Henry Maudsley, founder of the famous psychiatric hospital, wrote that spiritual leaders, including Mohamed, St Paul and Charles Wesley, experienced visions because they were epileptic. Only this week a neurologist at Bologna University proposed that Dante's visions were the result of narcolepsy.

From the standpoint of atheism, all experiences of the supernatural must be either delusional or fraudulent, and this applies to Jesus and St Francis as well as modern visionaries such as the Irish mystic Lorna Byrne.

But as I've tried to show in my new book, altered states of consciousness, in which the subject believes he or she is guided by supernatural intelligence, is not confined to narrowly religious fields. Great leaps forward in science, politics and warfare have often come about as a result of experiences which seem to defy rational explanation, whether the "daemons" that mentored Socrates and Jung, the Swedenborgian mysticism that guided Abraham Lincoln and Martin Luther King or the alchemical inspirations of Newton and Nicholas Tesla's invention of his coil, generating an alternating current. By the standard of atheistic psychiatry, these people were all either mad or at the least suffered psychotic episodes.

Perhaps the lesson of the Asda furore is this: on race, generation, gender and sexual orientation we have made great progress. But there is one grouping that cuts across all the others where we need to start moving forward, and that is toleration between different forms of consciousness.

Jonathan Black's new book 'The Sacred History' is published by Quercus