As with so much else in Britain, whether or not you believe evil exists depends on your class. Readers of the popular papers have few difficulties accepting that terrible crimes from the murder of James Bulger to the serial killings of Harold Shipman can be explained by evil. But even bishops who read the broadsheets - or the 'unpopular papers' as Kelvin MacKenzie, a former editor of the Sun, once unkindly suggested we should be called - become fidgety in evil's presence. George W. Bush lost what slender chance he had of winning over middle-class liberal opinion when he denounced the 'Axis of Evil'. Politicians who use the word are seeking to 'demonise' enemies by turning them into monsters, argue those who don't think that the leaders of North Korea and Iraq were capable of becoming monstrous without help from others. Tabloid editors are as calculating. They need a constant supply of monsters to keep the paying public in a profitable state of outraged terror.  There's a lot to be said for conventional liberal wisdom. It has been almost comic to watch the effort put into turning Maxine Carr into the next Myra Hindley. She seemed perfect for the part: good-looking in certain lights; dead-eyed; and, apparently, motivated by an unnatural desire to assist her cruel lover in whatever he wanted to do. The shameful spectacle of the Home Secretary rushing to rig the law to prevent Carr's early release from prison last week was the fruit of a lot of hard work by my colleagues. In the end, however, Carr will fail the horror-movie screen test. She didn't help Ian Huntley. She was one of his victims in her own small way: a regular recipient of his beatings. Prison officers, who don't tend to be among nature's bleeding hearts, describe her as a simpleton who is 'as daft as a brush' rather than a sinister manipulator. The Carr case seems to justify fastidious prejudices about the mob and the mob's newspapers. All the unwarranted attention she has received has done is ensure that she will need years of police protection from an ignorant public which has been maddened by a reckless media.  But the public isn't always as ignorant as the hounding of Carr implies. If its concept of evil didn't exist, it would have to be invented to cover the gap in all great crimes between understandable causes and inexplicable consequences.  Take the Bulger murder which dominated the crime debate in the 1990s and helped make Tony Blair Labour leader. All kinds of reasons were advanced to explain why Jon Venables and Robert Thompson slaughtered a toddler. They came from poor homes, their fathers had walked out on them, they had watched Child's Play II, and may have been inspired by the gruesome film. But honest journalists and detectives admitted at the end of the trial that none of the theories they advanced began to explain the cruelty of the killing. From what I hear from people who have talked to the social workers who looked after them in custody, Thompson and Venables can't explain why they did what they did either. There is a gap between cause and effect, and if you don't use the concept of evil to bridge it, you'll have to find another word with the same meaning.  The gap in the case of Thompson and Venables becomes a yawning chasm in the case of Harold Shipman. Because he never confessed, no one can adequately explain how the doctor became a mass murderer. The best journalists can do is say that he was driven to succeed by an ambitious mother who cosseted and petted him. Vera Shipman died suddenly when he was 17, and the shock of her death is meant to have pushed him into depression, drug-taking and, finally, murder. It's a rational theory but its proponents accept that it doesn't begin to account for Shipman's actions.  The families of the patients he killed didn't on the whole share the crass jubilation of David Blunkett and the Sun at news of his suicide. They felt that he had remained in control to the end, and dictated the terms of his own death as he had dictated the terms of the deaths of so many others. Many complained that they had been denied the chance of discovering why their relatives had been murdered. It's no disrespect to them to suggest that if Shipman had come clean, they probably wouldn't have heard an explanation which made sense.  The German-American intellectual Hannah Arendt gave the best reason why not when she invented the phrase 'the banality of evil'. (Her use of the word 'evil', by the way, can be excused by the fact that she was writing in 1961, an unsophisticated time when we hadn't learned that it was sinful to be judgmental.) The occasion for her outburst was the trial of Otto Adolf Eichmann in Jerusalem. He had organised the deportation of millions to Nazi death camps.  Arendt looked at him and was shocked to discover that 'the man in the glass booth was not even sinister ... The deeds were monstrous, but the doer was quite ordinary, commonplace, and neither demonic nor monstrous.' The worst she could say about him was that he had 'a curious, quite authentic inability to think ... When confronted with situations for which routine procedures did not exist, he was helpless, and his clich-ridden language produced on the stand, as it had evidently done in his official life, a kind of macabre comedy.'   Eichmann was just a good bureaucrat who obeyed orders. When he was in power, he committed unimaginable crimes; when he was on trial he was a shrivelled and ridiculous figure who didn't have the language to explain what he had done to himself, let alone to others.  Evil is banal. Time and again with mass murderers, people expect to see a demon who can inspire awe as well as fear, only to find that they are dealing with a babbling fool. I remember the stir among the journalists in Dunblane when the police announced that they would release copies of letters Thomas Hamilton had posted just before he walked into Dunblane Primary School and massacred 16 children and their teacher. We were sure that they would give us an explanation; a reason which would make sense of the senseless.  The letters turned out to be complaints against the Scouts, who had expelled him 20 years before for minor mistakes during a camping trip to the Highlands. There had been no public disgrace, nothing that could provoke murderous resentment in an ordinary man. Local organisers had simply decided that Hamilton wasn't up to being a Scout leader because boys under his care had gone back to their parents cold and wet after he had made them dig snow holes. Hamilton must have thought that when people read the letters they would understand why he had to commit an atrocity and then kill himself; that comprehension would lead to a posthumous pardon. The effect was the precise opposite: readers were mystified and contemptuous. All that for this?  Huntley, Shipman and Hamilton were petty offenders compared to the great criminals of our times. But the pattern remains the same. The shock which followed the arrest of Saddam Hussein was the shock of being confronted with banality. Here was a leader who had sent armies roaming across the Middle East, who had produced the death of a million in foreign wars and hundreds of thousands in domestic oppression, who had enforced a cult of the personality it was fatal to dissent from, who had forced four million people into exile, who had been indulged by the West, the Soviet Union and the Arab world and who was, at the end of a lifetime of terror, just a dirty old man cowering in a hole.  Like the families of Shipman's victims, Saddam's subjects will want an explanation. They're unlikely to get one from their former tormentor. Adel Abdul-Mehdi, a Shia politician, confronted the tyrant after his capture. What about the 300,000 corpses found in mass graves since the end of the war, he asked?  Like Hamilton, Saddam assumed that even the relatives of the dead would have to concede that there were good grounds for the executions. 'Ask their families,' he replied. 'They were thieves and they ran away from the battlefields with Iran and the battlefields of Kuwait.'  Ahmed Chalabi, the leader of the Iraqi National Congress, watched the exchange and noted that Saddam was 'not remorseful at all. It was clear he was a complete narcissist who was incapable of showing remorse or sympathy to other human beings.'  And that, I think, is about as near as you can get to defining evil. It is pure selfishness and pure thoughtlessness. Once a Shipman or a Saddam has been overthrown, the only point worth dwelling on is how on earth the rest of us let them get away with murder for so long.