It began when filmmaker Michael Moore appeared on Keith Olbermann's MSNBC show on 14 December, and was asked about his support for Julian Assange in the light of allegations of rape against the WikiLeaks founder. Moore replied:

This whole thing stinks to the high heavens. I've got to tell you. I mean, I wasn't born yesterday. But I've seen this enough times, where governments and corporations go after individuals … They go after people with this kind of lie and smear. Daniel Ellsberg told you about it last week how they went after him. We've seen this before. Now, [Assange's] guilt or innocence of this – I mean, what he said they did [sic] – and the lawyer said this today in court in London – that what they say he did and the charge is, his condom broke during consensual sex. That is not a crime in Britain, and so they're making the point, how can we extradite him over this? This is all a bunch of hooey as far as I'm concerned.

A week later, Moore reappeared on MSNBC to talk about the same subject. This time, Moore's message was dramatically different. Instead of diminishing the sexual assault allegations against Assange as "a bunch of hooey," Moore told Rachel Maddow:

Every woman who claims to have been sexually assaulted or raped has to be, must be, taken seriously. Those charges have to be investigated to the fullest extent possible. For too long, and too many women have been abused in our society, because they were not listened to, and they just got shoved aside … So I think these two alleged victims have to be treated seriously and Mr Assange has to answer the questions.

What changed Moore's tune? In the week between those two appearances came hundreds, if not thousands, of tweets, blogposts and Facebook entries, most of them organised around a Twitter hashtag – #MooreandMe – started by New York blogger (and Guardian contributor) Sady Doyle, along with Jaclyn Friedman.

And what #MooreandMe revealed is that the casual dismissal of the allegations against Assange has rightly angered many – explained in compelling detail by Kate Harding, Katha Pollitt and, in this remarkable essay, Andrea Grimes – who see it as a symptom of the struggles that women still face in being heard on the subject of rape and sexual assault. While the two women in Sweden have been disparaged as tools of the CIA, or derided as hysterical (and sometimes both at once), Assange and his lawyers can speak freely in public.

But worst of all has been the suggestion that somehow their ordeal does not count, that they are an inconvenient distraction, the mad women in the attic, caught up in the clash of powerful forces involving the world's media and the US government in all its might – as Moore put in on his blog on 14 December:

For those of you who think it's wrong to support Julian Assange because of the sexual assault allegations he's being held for, all I ask is that you not be naive about how the government works when it decides to go after its prey. Please – never, ever believe the "official story". And regardless of Assange's guilt or innocence (see the strange nature of the allegations here), this man has the right to have bail posted and to defend himself.

Melissa McEwan noted: "Would that he had left it at the right to bail and defence and skipped the rape apologia."

Once upon a time, that might have been it. But Moore's callous remarks, which passed without challenge by the normally pugnacious Olbermann, caused a reaction that found full-throated expression through social media. Objecting to Moore's offhand dismissal of the allegations, Sady Doyle explained it in her post launching #MooreandMe:

You know what immeasurably harms the progressive community, though, is rape and rape apologism. Is victim-blaming; is accuser-smearing; is the unwillingness of men in positions of power to consider rape a crucial issue that must be taken seriously. And the person who's hurting our community, and refusing to take responsibility for that, right now, is Michael Moore. So thank God he's on Twitter. He is @MMFlint, in fact! And here's what we're going to do: we're going to use the #MooreandMe hashtag to tell him why what he has done and said is wrong. We're going to talk to the man. We're going to stand outside his window with a megaphone until he comes down and talks to us.

And that, pretty much, is exactly what happened.

For a week, Moore didn't respond to the tide of protest. Olbermann did, foolishly and petulantly, only to make matters worse – boasting that "Feminism has no greater male supporter in TV news than me", and at one point proclaiming he was suspending his Twitter account "until/if this frenzy is stopped", although he failed to take his own good advice.

Other writers waded in and got caught in the fallout: the journalist Moe Tkacik posted at the Washington City Paper, describing #MooreandMe as "near-homicidal #rage" while naming the two women (something the Guardian and New York Times have avoided as a matter of policy), only for her editors to yank the piece. The blogging pioneer Dave Winer produced an artless car-crash of arguments that might have worked as parody. Naomi Wolf continued her upside-down defence of Assange – as can be heard in her debate with Jaclyn Friedman on Democracy Now. And so on.

In the end, though, it was Moore – without addressing #MooreandMe directly – who gave way, with his appearance on Rachel Maddow's show. Olbermann, meanwhile, like a soldier marooned on a Pacific island who doesn't know the war is over, sits nursing his wounds, and making gnomic statements and half-apologies.

Moore had the decency to send a message – via Twitter, appropriately – directly to Doyle on the night of his second MSNBC appearance, saying:

Thanks & Merry Xmas 2 you! Sorry I didn't respond sooner. I needed more than 140 charcters 2 say what I said 2nite - & it needed 2 b said on TV

To Doyle should go the last word, on how a hashtag harnessed a groundswell of protest:

That's the most important lesson of #MooreandMe, for me, the most important takeaway: the next time something is this fucked up, and we feel like we have to fight it, we will. The next time we feel like we have to fight something, we will know fighting can make a difference. The chief thing #MooreandMe gave me, the girl who started out a week ago just writing an irritated Tweet and then eventually hearing a "thank you" from Michael Moore, was faith in the idea that activism can change things.

• Author's note: for full disclosure, in my former role as editor of Comment is free America, I commissioned Sady Doyle to write opinion articles for the Guardian