Few subjects are as contentious, or as poorly understood, as rape. Blaming the victim is common, as is endlessly finding excuses to "explain" why some men brutalise women. Three months ago, people used social networking sites to abuse – and name – a 19-year-old woman raped by the professional footballer Ched Evans, who had just been sent to prison for five years. Last week, at Cambridge Crown Court, a schoolboy was spared a custodial sentence for raping a five-year-old girl after he blamed his "hormones" and the judge blamed "the world and society".

Most rape cases are horrible, this one particularly so. The boy, 14 at the time, was known by the girl's parents who asked him to babysit while they went to watch an older child in a school play. On their return, they paid him £10 and he went; it wasn't until the little girl was getting ready for bed that she told her father what had happened. On Monday, the judge imposed a three-year community sentence with a supervision requirement on the boy, leaving the victim's parents to worry about the possibility that she will bump into him on the street. The girl's mother said the sentence sent the "wrong message" about rape, and could deter other victims from coming forward.

She is right. Counsellors and campaigners talk about "myths" which blur the definition of rape and encourage misconceptions, such as the idea that attackers are "provoked" by the victim's clothing or behaviour. Both the courts and the media repeatedly look away from the individual assailant, whose responsibility for the crime gets lost in a welter of excuses. Anyone who rapes a five-year-old is by definition a danger to girls and women, who are entitled to expect protection from the criminal justice system.

The judge mentioned the boy's use of internet pornography, claiming his exposure at a young age had ended in "tragedy" – a strange choice of word for a vicious assault – but a 14-year-old boy is old enough to know that forcing someone to have sex is a crime. If he goes ahead and does it anyway, he belongs in a subset of sexual predators who will have violent relationships with women when they grow up.

The case underlines the need for education about sexual violence, both to protect potential victims and to identify boys with aggressive attitudes to sex. Parents and teachers need to be on the outlook for such young men, and challenge their behaviour at an early stage.

It doesn't happen often enough. Everyone thinks rape is a bad thing in theory, but real-life cases are very different. Total strangers rush to excuse rapists on Twitter, while no one believed the victims of the black-cab rapist, John Worboys, leaving him free to drug and rape more than a hundred women in London over a period of years. We should worry about lenient sentences and ambivalent public attitudes, which mean rapists aren't sufficiently afraid of being condemned and punished.

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