Theodore Dalrymple has a sobering look at the power of evil: Nick Berg’s executioners all too clearly enjoyed beheading him. (Hat tip: mal.)

One thing that unites the men who beheaded the American Nick Berg in Iraq, the soldiers who abused Iraqi prisoners in Abu Ghraib, the Palestinians who have held on to Israeli body parts in Gaza City and the murderers of Daniel Pearl in Pakistan is that they all enjoyed what they did, and enjoyed it immensely.

There is almost no greater pleasure known to man than to commit great acts of cruelty in the belief that the cause of right and justice is being served. Anyone who has observed rioters will know that they are having a wonderful time: could there be a greater joy than vandalism with a social purpose?

I used to wonder how it was possible for ordinary men to commit evil acts, and to do so en masse. I was thinking of Nazi Germany at the time, but I might just as well have been thinking of the Soviet Union. More recently, we have the example of Rwanda, where perfectly ordinary people who had been living in apparent conditions of friendship with their neighbours suddenly turned on them and hacked them to death with machetes.

There are a few exceptional human beings who seem to delight in evil all their lives. It is as if there is some inherent or acquired defect in their brains that renders them unable to learn the decencies of life or conform themselves to the canons of civilised behaviour.

From the earliest age, they stand out by their capricious and cruel wilfulness. They delight in torturing animals, dousing them in kerosene and setting them alight, or putting them in the washing machine; they lie and cheat for preference, even when there is no advantage in doing so. They are indifferent to the opinions and sufferings of others, and never learn to modify their behaviour from their own experience.

They are what the 19th-century alienist J. C. Prichard called “morally insane”: they are neither deluded nor hallucinated - they may even be of good intelligence - but they are incapable of internalising a moral code and of conforming their conduct to it.