The symbol of this Christmas is the noose. Hang my son, says Ian Huntley's mother. Hang Saddam, says almost everyone. The gallows is not an option for Maxine Carr, who is due out of jail next May. The relatively minor nature of her sin, a crime of lies and silence, has not prevented Maxine-haters placing her in a continuum of female she-devils stretching from Medea to Myra. As the great Judaeo-Christian feast approaches, the polarity between good and evil is stark. In modern replays of the Book of Genesis, conducted in settings as diverse as the Old Bailey, a spider hole near Tikrit and your local Odeon, light does not often vanquish darkness. For happy endings, try Philip Pullman's Dark Materials trilogy at the National Theatre or Tolkien's Return of the King.  In real life, evil prevails. Despite George W. Bush's masterclasses on the subject, there is no particular hierarchy of monsterdom. Michael Jackson, facing child sex-abuse charges, may get a politer welcome on his planned visit to the UK than the one extended to the God-fearing President of the United States. Nor is there an obvious logic to the way we treat untouchables.  Saddam's capture inspired a desire for vengeance, certainly, but also an uneasy pity. The dead eyes and prophet's beard drove commentators to plunder the Old and New Testaments as thoroughly as Bush's speechwriters in an effort to discover what their unexpected sympathy represented. The non-religious answer is what Hannah Arendt called the banality of evil.  Tyrants and murderers are defined not only by evidence of their actions - in Saddam's case, the toll of Kurdish citizens gassed and of skulls scratched up from mass graves - but by a cruelty of the imagination. Myths of how maniacal despots behave sit uneasily with Saddam's domestic inventory: one can of 7 Up, a bottle of Lacoste Pour Homme cologne, minted toothpicks, Maxwell House coffee and a picture inscribed 'God Bless Our Home'.  The humdrum detail that jars the observer out of unadulterated hatred also operated in the case of Ian Huntley. His conviction for the murders of Holly Wells and Jessica Chapman was a restrained affair, free of mobs storming the courtroom precinct or screaming 'Kill Him', in an echo of Tyburn. There was little sign of the bloodlust that followed the Moors Murders and the sentencing of James Bulger's killers. Yet few murders have transfixed Britain, and the world, like those of Holly and Jessica.  Their deaths fed a fear corroding society. If two little girls in smalltown England could be lured to their deaths by a trusted neighbour, then no son or daughter is safe. But more than one child is slaughtered every week by a parent and no one notices. Skewed notions of risk are driven by rare crimes and normally articulated in mob venom.  One reason for a more subdued response might be the dignity of the Chapman and the Wells families, who forbore to demand vengeance. In addition, people do not know, and perhaps never will, exactly how the children died. But those facts do not explain why Huntley has escaped bestial status. I asked a hairdresser friend who has been canvassing her clients. 'It's because he looks so normal,' they told her.  Presentability served Huntley well. His convincing manner persuaded underage girls to have sex with him and prosecutors to ignore their cries of rape. The post-trial furore has been directed at police error in logging past complaints against him, but this is not primarily a scandal of bad filing. The lack of heed paid to his record reflects a society that extended more credence and legal rights to plausible men than to abused girls. Even now, if a case is to succeed, prosecutors prefer their victims dead.  The authorities and the public want child molesters to look like proper perverts, in the mould of a snaggle-toothed Roy Whiting, Sarah Payne's murderer, who appeared in the Sun last week under the headline 'Grinning Creature'. Resembling Jack Nicholson in the latter stages of The Shining saves confusion. Irrespective of bureaucratic bungling by police, Whiting was never school caretaker material. He is separate, a monstrous other who, unlike Huntley or Saddam, holds no Caliban's mirror up to the virtuous world. Pious people, along with neglectful officials and prurient newspapers, need not worry about the thin dividing line between the demon and the normal citizen.  Since the Soham trial lacked a monster from central casting, Maxine Carr gets the role. A fellow prisoner has thrown boiling water at her, and the media hold her guilty of murder by proxy. On the night of the killings, Carr was at a party. The outing might, her critics claim, have pushed a jealous Huntley over the brink. 'Kiss of death' screamed the headline over a picture of her embracing a fellow reveller.  That snapshot in a Grimsby disco placed Carr in a pantheon of female monsters, ranging from the Harpies and the Sirens of Greek legend to Rose West. In myth and in distorted reality, women, deadlier than the male, occupy a spectrum between psychopathy and culpability for engineering family breakdown and producing delinquent children. Carr, branded the 'new Myra' and the catalysing agent of evil, was actually a liar whose mistake was to shack up with a murderer.  In being duped by Huntley's charm, she resembled the police, the school staff, the community and the two trusting girls he murdered. She behaved as others might, and for that reminder of our fallibility, more than her mendacity, she can never be forgiven. In a universe where religious language and political discourse collide, Carr is banished forever from the civilised world to reside with the ranks of the dark forces. Their quarters are becoming more cramped than Saddam's bunker.  The expanding army of darkness encompasses murderers and their gullible girlfriends, along with leaders of Iran and North Korea, the shapeless prosecutors of terror and the suspects interned without charge at Guantanamo and Belmarsh. Arbitrary polarities of good and evil, patented by politicians, mesh with a vengefulness in public thinking.  The capital punishment debate stirs again. Huntley should be executed, according to the string-'em-up lobby whose ambitions will never be heeded by any mainstream political party. Hanging Saddam, however, is deemed perfectly acceptable in Downing Street and the impeccably liberal leader columns of the Independent.  Merciful democrats cannot have it both ways. Certainly, Saddam should be tried in Iraq, but for Britain to rubber-stamp a death sentence would be disgraceful buck-passing by an occupying power which must now stand by its principles. Either we support what David Blunkett calls 'judicial murder' or we recognise that the first test of a humane society is the way it treats the most hideous.  Saddam, like Huntley, should spend his life in prison. There they can suffer for their crimes while offering an enduring reminder to those who once armed a tyrant and failed to stop a potential murderer. Denouncing evil is easy. How much harder to recognise that monsters, with their French cologne and high street clothes, not only share our tastes. Good societies must also shoulder some fragment of their guilt.