For the howling mob, the woman is more evil than the man

He is "the caretaker", safely immured in the country's most secure hospital, where even the most determined vigilante cannot reach him. She is Maxine Carr, public enemy number one, isolated for her own protection in Holloway, one of the country's grimmest prisons. On Friday Carr's mother, Shirley Capp, said her daughter was "terrified".

Such are the contrasting fates of the couple at the heart of the investigation into the murders of two 10-year-old girls, Holly Wells and Jessica Chapman, from Soham, Cambridgeshire. This dreadful crime, and the sensational way it has been reported, has stirred up powerful feelings. "Maxine hasn't been charged with murder, yet she's being treated like a killer," her mother protested last week.

Carr, a former classroom assistant at the school attended by the victims, is charged with attempting to pervert the course of justice (though she may yet face more serious charges). It is solely her boyfriend, 28-year-old Ian Huntley, caretaker of Soham Village College, who has been charged with the murders. He has also been sectioned under the Mental Health Act. Yet it was 25-year-old Carr whose appearance at Peterborough magistrates court on Wednesday was greeted with unrestrained fury.

"A life for a life" and "Rot in hell" were two of the milder messages as the police van in which she was travelling was pelted with eggs and bottles. Mothers screamed "Scum" and "Bitch" while small children sobbed and clung to each other in terror, apparently failing to share their parents' view that witnessing such a spectacle was an educational way of spending the school holidays.

Members of the mob hotly denied that such exposure was itself a form of child abuse. "They're not afraid of all this," claimed one woman. "They're frightened to walk the streets." Another public-spirited citizen, who has a four-month-old son, hurled an egg at the van. "That woman is scum, she should be let out of prison and the public can deal with her," declared 28-year-old Rhonda Bailey.

These demands for summary justice were ignored – as was prima facie evidence that members of the crowd were committing a variety of offences, including using threatening behaviour and breaching the peace. Inside the courtroom, Carr disappointed some of the journalists present who, frustrated by reporting restrictions, fell back on the old ploy of reading the character of the accused from her demeanour during the hearing.

Being driven through the mob "didn't seem to have affected her too deeply", concluded the Daily Mail's expert observer. "Her eyes remained closed for a while after she sat up, and everyone craned to see if there were any tears. There were not."

The paper also reported that the corners of Carr's mouth "turn down like a moody teenager's, and her dark eyes have a permanently distant look."

This is prejudicial stuff, implying that Carr feels no remorse at a time when all that is publicly known is that she is accused of lying to detectives during the investigation into the girls' disappearance. It is also wearily familiar, calling to mind the abuse heaped on Primrose Shipman when her husband Harold, now regarded as this country's most prolific serial killer, was tried for murder.

Crime correspondents rarely remember the old adage about not judging by appearances. It is a fair bet that few of us would appear at our best in court, after days of police questioning, although we might muster sufficient self-control – unlike the adrenaline-fuelled vigilantes outside the courthouse – to avoid breaking down altogether.

But the threats and insults are revealing for other reasons. One is the speed with which women become tainted with guilt by association, even when they face lesser charges than their husbands or boyfriends – or none at all, as in Mrs Shipman's case. Even in those rare instances where a couple face identical or similar charges, it is the woman – Myra Hindley, most notoriously – that everyone remembers. Female serial killers are very rare and when they do turn up, there is usually a sado-masochistic relationship in which the woman has been brutalised and corrupted by her male partner.

Yet time and again these women become, in the words of Helena Kennedy QC, "the vessel into which society pours its dark secrets". This is not to excuse the crimes of Hindley or Rosemary West, but it is to suggest that our culture manifests a recurrent yearning for scapegoats. There is a great deal of ambivalence about male violence, whether it takes the form of excusing wife-beating or B-list celebs turning out in droves at the funerals of gangsters like the Krays. But everyone agrees that women are supposed to be nurturing and maternal, which makes violent women easier to condemn – and to distance from the rest of us.

There is also a reluctance to face unpalatable facts, such as the consensus among experts that children in this country are far more at risk from members of their own family than they are from roving gangs of paedophiles. According to Mary Marsh, director of the NSPCC, "the vast majority of the one or two children who are killed each and every week in Britain die at the hands of parents and carers".

Last week's scenes at Peterborough magistrates court and on a Bournemouth housing estate, where women claimed to have identified 17 paedophiles, are ways of not facing this unpleasant reality, which undermines comforting myths about the family. In that sense, the cry of "stranger-danger" – almost always the focus of campaigns against paedophiles – can be seen as a way of deflecting attention away from the abuse that happens in the home.

It is also a manifestation of mass hysteria, reminiscent of the wild allegations about witchcraft that led villagers across Europe four centuries ago to burn unpopular women at the stake. Some newspapers bear a heavy responsibility here because their prurient reporting of the Soham disappearances was always likely to lead in this direction. Sentimentality and viciousness go together, as the mothers who joined the mob to "protect" their children reminded us last week. What they were really doing was advocating forms of retribution almost as barbarous as the crimes they claim to despise.

Capital punishment is not a deterrent to child murder, as American experience proves: the number of child murders has risen in the US, from 896 a year in the mid-1970s to 1,311 in the 1990s. The increase coincides exactly with the period in which a majority of American states re-introduced the death penalty, using it most enthusiastically in emotive cases such as the abduction and murder of children.

None of this is likely to make much impression at a time when, excited by a sense of outrage and misplaced moral certainty, vigilantes are looking for paedophiles round every corner. On Friday, The Sun printed a selection of messages from readers, some of which claimed, "You cannot count on British justice to give paedophiles what they deserve" and "We've just given our children to them with our liberal laws and punishment system".

This is hysterical rubbish, which editors should be ashamed to publish. The murders of Holly Wells and Jessica Chapman are horrifying, and a ghastly tragedy for their families. But child murders remain relatively rare in this country, with experts suggesting last week that the rate has remained constant or even gone down in recent years.

Of course it makes sense to look again at child protection procedures, such as vetting adults who apply for jobs working with children. But if we are a sick society, as some commentators have suggested, we should not be adducing as evidence highly unusual crimes like the Soham murders. If it is to be found at all, it is in the disgraceful scenes surrounding Maxine Carr's court appearance, when hundreds of ordinary people behaved like a howling lynch mob.