It’s one of those slogans that are well-intentioned, and memorable, and utterly wrong: “Rape is about power, not sex.”

After Harvey Weinstein’s conviction last week on one charge of rape and one of a criminal sex act, the phrase predictably made its appearance among the op-eds and commentary. And there are very good reasons for both its existence and its persistence. Drawing a hard, sharp line between “sex” and “power” was one of the strategies that the women’s movement used in the 20th century to undermine the patriarchal narrative about rape.

In the he-said, she-said, no longer could he say that he did it because he was so inflamed with desire for her (or that he didn’t do it because she was too ugly to rape, or couldn’t have done it because she was too easy to ever say no). By making the case that rape was a crime of power, not passion, feminists were able to shift rape trials away from being inquests into the attractions and virtues of the victim.

That shift is incomplete, and for many women, prosecuting a rape ends up redoubling the trauma and invasion of the original attack. Even so, it is at least understood in principle that a rape trial is about consent and not propriety. The sex/power divide does something else as well: it helps to protect women’s experience of their own sexuality from the fact of endemic exploitation. It says that, even in a world where men use sex as a weapon against women, it’s possible to mark out something of your own, a walled garden of pleasure where inequalities of power do not apply.

We have to reckon with this – the fact that there are men for whom the resistance is the thrill

All these things matter. Unfortunately, “rape is about power, not sex” has one very significant demerit as a vehicle for women, which is this: rape is, obviously, very much about sex. It’s a turn-on for the rapist. If it wasn’t, he wouldn’t be able to commit his crime. Had Weinstein simply wanted to exercise power over the women he employed, he had plenty of ways of doing it that didn’t involve his penis. For the rapist, the sex and the power are indivisible.

Rape is never a simple misunderstanding about the meanings of yes and no. (One of the absurdities of rape trials is that they so often hinge on the accused man claiming a kind of incomprehension, which, if applied to any other realm of human experience, would make communication impossible: we can all tell, via myriad cues of context and non-verbal negotiation, when someone is taking a gentle pass on what we’re proposing. Only when it comes to sex does it apparently become necessary to give explicit refusal.) For the rapist, the lack of consent is the point.

We have to reckon with this – the fact that there are men for whom the resistance is the thrill; for whom knowing that they’re not wanted and doing it anyway is what gets them going. And we have to reckon with it, because as long as we sustain the pretence that “power” and “sex” are concepts that can be safely separated from each other, we are inadvertently giving cover to the exploitation of women.

Women, as a general rule, are less powerful than men. Less powerful physically (Weinstein’s appearance in court as a frail old man relying on a walker is at contemptible odds with his victims’ accounts of him using all his advantages of height and bulk to corner them), but also less powerful politically, financially and socially. When Weinstein’s defence argued that his victims were not victims because they needed something from him, his lawyers were making an argument that belonged properly to the prosecution. He could destroy the careers and reputations of women who displeased him, and he did destroy them. What does “yes” even mean in that context?

The same question applies whenever sex is turned into a transaction: what does “yes” even mean? When a man pays a woman to have sex with him, or a woman is paid to have sex on camera for the purposes of pornography, what does “yes” even mean if saying “no” would stop her from affording rent or eating a meal? And when a man gets his sexual pleasure from a woman whose consent has been bought – whether that’s by directly having sex with her, or by getting off on watching someone else have sex with her – part of that pleasure comes from the power that he enjoys over her.

The #MeToo movement sparked by Weinstein’s exposure has become a rallying point for contemporary feminism, but it’s a movement still deeply divided over what gets called the sex industry. There are activists who will condemn sexual harassment in one breath and in the next defend pornography and prostitution, as though they believe that the industries that rely most of all on sexual commodification are somehow uniquely free from abusive practices. The false divide between sex and power enables this dishonesty: by convincing the world that its business is desire, the sex industry has won an exemption from having its abuses of power examined.

Cinema’s confrontation with its own misogyny has begun, haltingly. The fact that Roman Polanski received three César awards – France’s equivalent of the Oscars – last week, despite his conviction for unlawful sexual intercourse with a 13-year-old, shows how much further that confrontation still has to go. But none of us can pretend to innocence any more: watch a Miramax film and we all know now that we’re watching the product of one man’s ability to exert his sexual will over women. Whatever is left to be enjoyed of those movies, we know what the body count was. Now do that sum for every business that makes its money from female flesh.

• Sarah Ditum is a writer on politics, culture and lifestyle