After 20 years in journalism there aren't many things I find it impossible to read about or watch on the news, but every time Grace Millane's parents' appeared on TV at the weekend, I had to leave the room. Broken and sobbing at the end of the three-week trial that found a 27-year-old New Zealander guilty of murdering their 21-year-old daughter, Gillian and David Millane knew that their life sentences were only just beginning. And yet they stood on the steps of Auckland High Court on Friday – where a jury had taken just five hours to deliver a guilty verdict – and paid tribute to the "beautiful, talented, loving daughter" throttled to death after a Tinder date.

Over the past three weeks the Millanes have been forced to listen to some painful testimonies from witnesses like Grace's ex-partner – who admitted that the couple had researched choking during sex – and a man "naïve and trusting" Grace had contacted on a BDSM dating site and told of her interest in bondage and being a "submissive slave." But what the the defence said will have been far worse for her parents to hear. Grace's killer – who cannot be named for legal reasons – did all he could to convince the jury that her death was an accident during the "violent sex" Grace had enjoyed and encouraged as a "fan" of the Fifty Shades of Grey films.

That he should have referenced E.L.James' erotic trilogy directly is itself no accident, say campaigners, who warned yesterday that thanks to an increasingly popular defence strategy known as "the Fifty Shades of Grey defence", men are being given a "free pass" to "accidentally" murder their partners during "consensual rough sex."


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Several legal reasons Grace Millane's killer continues to have name suppression

The number of cases where this defence has been used has increased tenfold since 2000, the campaign group We Can't Consent To This pointed out, with half of those alleged killers convicted on lesser charges than murder – and two cleared. And if you count the headlines, it's true that over the past fortnight alone the "Fifty Shades Defence" has been used nine times in murder and assault cases involving British women.

Female victim-blaming in sex crimes is a time-honoured tradition that plays into the long-propagated narrative that women should be punished for being 'promiscuous' or 'deviant.' Only today Grace would neither be considered more promiscuous than your average 21-year-old, nor deviant. In fact the "Fifty Shades defence" is probably the 2019 version of the preposterous "short skirt defence."

Because although older generations may balk at the kind of language being exchanged online by women and men far younger than Grace, with even mainstream dating websites like Tinder allowing BDSM tendencies and an enjoyment of 'rough sex' to be stated in users' profiles alongside their hobbies, we have to accept that this is now commonplace.

Focus Live Earlier: Family of Grace Millane speak after guilty verdict.

What we can and should ask, what can be done to safeguard the many equally "naïve and trusting" women who are going in search of sexual adventure online as I write. When I interviewed British forensic psychologist Kerry Daynes earlier this year, she informed me that a terrifying number of "both boys and girls now believe that crying is a natural part of sexual foreplay. That's how much young people believe rough sex is the norm." But it was the words Daynes used as she explained that the authorities were now seeing an increasing number of younger sex offenders with no histories of abuse that really stuck with me: "society has done the grooming for them."

With the kind of extreme pornography younger generations have been raised with, it's no surprise that both male and female sexual expectations are very different to what they were 50 years ago. Add to that an online culture promising to cater to every desire, and you have a terrifying brave new world where dangerous men can prey on vulnerable women at the click of a button.

As the founder of We Can't Consent To This, Fiona MacKenzie, points out, we're now in a place where the normalisation of violence against women in sex "means that in a court case, violence can now be something you 'consent' to", and "the Fifty Shades of Grey defence" is being used as a "get out of jail free card." Which would make it less of a brave new world and more of a devil's playground - where the real deviants, miscreants and monsters are allowed to murder young women like Grace and roam free.

We can but hope that the twelve jury members who refused to give Grace's killer that 'get out of jail free card' have set a precedent that will start to reverse this tragic trend.