She sounds like the stuff of a middle-aged man’s nightmares; a stalker who simply wouldn’t leave Stuart Kerner alone. She had targeted him, the judge said sternly, at an “emotionally vulnerable” time; it was almost as if she was grooming him.

Reading the court reports, you have to pinch yourself to remember who is the victim here. Yet for the record, the defendant wasn’t the troubled 16-year-old girl thus portrayed but her 44-year-old teacher, who by sleeping with her had broken the law. (For teacher and pupil – or any other relationship involving an adult who is in a position of trust – the legal age of consent effectively isn’t 16 but 18.)

Oh, and if you’re wondering why the judge deemed him “vulnerable”, it’s because his wife had had a difficult pregnancy; the week she miscarried, he slept with his student. Which does raise the question of who, exactly, was vulnerable to whom.

This is the sort of story that makes one weary, deep down in the bones: oh Lord, not this again. So much for training judges to discard the victim-blaming myths with which they may have grown up; so much, arguably, for trying to diversify the judiciary when this verdict was handed down by a female judge, Joanna Greenberg QC. The only bright spot is the flurry of complaints it has attracted, although it emerged yesterday that the attorney general is powerless to refer the sentence for review despite complaints that it was too lenient (Kerner was convicted on two counts of sexual activity with a child by a person in a position of trust, but received a suspended sentence).

But there will still be plenty of people, not all of them lecherous old gymslip fantasists, who won’t get what the fuss is about; who think it’s inevitable that the odd teacher, surrounded by surging adolescent hormones, will give in to temptation.

It’s true that you’ll never stop teenagers having crushes on their teachers, and nor will you ever stop some teachers secretly fancying their sixth-formers right back. But that’s not the point. It is acting on desire, rather than merely feeling it, which is criminal – and any teacher prepared to break the law for a fumble behind the bike sheds should be nowhere near a classroom. This whiny, couldn’t-help-myself nonsense needs to stop.

It’s not hard to see why the myth of the predatory minx, in whose hands all are helpless, might appeal to men: it is, sometimes quite literally, a get-out-of jail-free card. But it’s surprising how many intelligent women buy into it too.

Shirley Williams said this week of her adored but unfaithful first husband Bernard, who left her for another woman, that he was “always a bit …vulnerable”. Because he was clever and good-looking he had been, she explained, “pinioned by quite a number of – I have to say – hopeful ladies”. Poor helpless Bernard: what chance did a mere moral philosopher have against those odds, eh?

Williams was talking, of course, about a relationship between two grown adults. But there was something sad and disconcerting about hearing her make such excuses for him. It’s all too easy for discarded wives to blame the other woman, rather than the man who so painfully betrayed them. But to do so is to accept the dubious idea that men are mere helpless slaves to their urges, while women are the ones who really ought to know better (and therefore to take responsibility when it all goes wrong). And where all this gets very, very toxic is when the “other woman” is little more than a child.

Those who mutter that a 16-year-old schoolgirl is surely old enough to know what she’s doing, whatever the law says, simply give succour to creeps with a dubious interest in ratcheting down the age at which seduction becomes socially acceptable. What if Kerner’s pupil had been just 15? Or 14, but sophisticated for her age? How young would she have to be before she could be seen as the child she is; before a come-on might be seen not as temptation but a reason for concern?

This girl, according to the judge, was “vulnerable and needy and had a troubled home life”; she had a history of attention-seeking behaviour, including pretending to have been in an accident. She sounds, in other words, not a million miles from some of the girls we now know to have been singled out for abuse by gangs of older men in Rotherham, Rochdale and elsewhere. You can’t condemn the authorities in those cases for failing to see through the confusion of a mixed-up, exploited kid who describes her abuser as her boyfriend, and then just shrug when a deputy head fails to see something unhealthy in a troubled 16-year-old’s adoration.

Perhaps she was, as the judge said, manipulative. But kids are manipulative; if they weren’t, this whole parenting thing would be a breeze. And if we don’t tolerate teachers giving in to their feelings when facing provocative behaviour that isn’t sexual – say, by walloping a thoroughly annoying child – then there is no reason to make lame excuses for someone who can’t suppress their desire long enough to teach double geography.

Any teacher who can’t put a child’s welfare above their own sexual gratification is in the wrong job – and those who still don’t see why need, quite frankly, to grow up.