Of course the women's march won't change anything – but that's not why we're doing it

I usually avoid protest marches. They are noisy, undisciplined affairs. Everyone has a different reason for turning up. Somewhere, a fringe group with a divisive agenda always manages to steal the attention and appropriate the message.

All these things may prove true today of the women’s march in London, or of any of its partner marches across the globe. All these accusations have already been levelled by its detractors. But a groper-in-chief is now President of the United States. So today, I’m marching with my sisters.

Allow me a thought experiment about President Donald Trump. Forget, for a moment, those murky trails suggesting Russian espionage and cyberwarfare – who are we to prove their complexities? Forget, just briefly, that sinking sensation you felt in your stomach as he stoked white America’s resentment against the foreign-born, the multiracial, the stranger. Forget those questions about his financial interests, and forget the nasty rumours that he can’t even manage to read a policy document.

What is left of Donald Trump? On what grounds can we indict him without question? To what crimes has he himself confessed? He enjoys sexual assault.

“Grab them by the pussy.” By the pussy. In Trump’s own voice, on tape, we heard him reduce each American woman to a fumblesome flab of flesh between her legs, a reluctant prize to be claimed by the winners of The Apprentice in a zero sum game. This isn’t an aberration from Trump’s life philosophy. Selling a lifestyle – whether a beauty pageant or aspirational business education – he has always preached sexual predation as the prerogative of the alpha male. This is the sexual prosperity theology of Donald Trump.

Most women have encountered men like Trump. Those who mock us for our naivety – “this happens all the time” – miss the point. We know this is the way of world. We know that Trump’s voters felt that boasting about sexual assault didn’t disqualify him from the White House. But we reserve the right to deplore the world in which this can be true.

As one woman told me the day after Trump’s election: “It feels like every man who has ever sexually assaulted me; every man who has harassed me on the street; every man who has demeaned me at work – they’ve all been cloned together, patted on the back, and handed the keys to the White House.”

On the Billy Bush tapes, Trump was seen talking about a specific woman, Arianne Zucker, who then immediately showed up to work with him. It confirmed everything women always suspected and couldn’t prove when we leave an all-male meeting room and hear laughter. Yes, “locker room talk” happens in every business environment. And, no, that’s not OK.

A march of angry women in London won’t change anything. Even a march in Washington DC will change little. The democracy of the American republic is to be treasured – if, to quote Benjamin Franklin, you can keep it. But women aren’t marching today in the hope of overthrowing a President. We’re marching because the only other option is to scream silently into our pillows every night.

It’s striking how many critics have emerged to police women’s anger. It is true that the left’s fierce policing of social language, the purity politics surrounding race and gender, have contributed to the polarisation of American and British politics. But it is not an excess of political correctness to be horrified by a sexual predator in the White House.

Few activists marching today hold out real hope that we’ll bring Donald Trump down. We simply cannot stay silent.