Alas, poor Milo Yiannopoulos, we hardly knew ye. Well, actually, that's not true. I first encountered Yiannopolous in 2012, when he tried to slut-shame a friend of mine, sex blogger Zoe Margolis, after she criticised his tech site, the Kernel. "We write about how tech is changing the world around us," he tweeted. "You write about how many cocks you've sucked this week. Back off."

It was a typical Milo performance. Flashy, provocative - and steeped in misogyny.

Fast-forward five years and he had managed to parlay those qualities into a gig with Breitbart, a public speaking tour, and until yesterday, a $250,000 book deal with Simon & Schuster. But last night, that was cancelled, "after careful consideration". Yiannopolous's invitation to speak at the Conservative Political Action Conference had been cancelled hours before. Over the years, CPAC has hosted Ronald Reagan, George W Bush and all the Hall of Fame right-wing blowhards: Glenn Beck, Rush Limbaugh, Sean Hannity.

What changed CPAC's mind? On 18 February, the organisation had tweeted that "free speech includes hearing Milo's important perspective".

We think free speech includes hearing Milo’s important perspective. #CPAC2017 pic.twitter.com/ssDS6HVmLN — Matt Schlapp (@mschlapp) February 18, 2017

Milo's important perspective on what was left unanswered, because it is unanswerable. Does anyone, really, think that Milo Yiannopoulos has deep and rigorously researched convictions? That his statements on feminism, on transgender people, or his criticisms of Ghostbusters actor Leslie Jones, spring from some deep well of evidence and sincerity?

Do me a favour.

Yiannopoulos was invited to CPAC to do what he does: be outrageous. To give the attendees a frisson of excitement at being in the presence of someone so notorious, someone willing to "say the unsayable". To outrage the left, and remind those watching of the gulf between them and the people waving placards outside.

Except the provocateur is finding out that some things really are unsayable. Some things - all his previous things, in fact - are extremely sayable, as long as you have the protection of the mainstream right and a media industry which craves - and monetises - attention. But a few are not.

So what did Milo Yiannopoulos actually say to prompt this outbreak of condemnation, and the withdrawal of lucrative marketing opportunities? The first thing to note is that the comments which kicked off the latest row are not new. After he appeared on Bill Maher's show improbably dressed as Like A Virgin Era Madonna (in an appearance up there with Jimmy Fallon rustling Trump's tawny locks on the Vom-O-Meter), old YouTube videos surfaced which, in the BBC's words, "showed him discussing the merits of gay relationships between adults and boys as young as 13". He said that the age of consent was "not this black and white thing" and relationships "between younger boys and older men … can be hugely positive experiences".

He has since denied endorsing paedophilia, said that he is a survivor of child abuse himself, and added that the videos were edited to give a misleading impression.

In the tweet announcing that he had been dropped, CPAC accused him of "condoning paedophilia". But he argues that elsewhere in the video he said that the US age of consent was in the correct place.

For those on the left, the overwhelming reaction to all this has been: why now? Why these comments, not the ones about "preening poofs", or lesbians faking hate crimes, or the danger of Muslims, or the harassment campaign against Leslie Jones which got him permanently banned from Twitter? (Do you know how consistently and publicly awful you have to be to get banned from Twitter???)

There's only one answer to that, really: yesterday marked the moment when Milo Yiannopoulos ceased being an asset to the mainstream right, and became a liability.

***

On 8 February, Jan-Werner Muller wrote a fascinating piece for the FT in which he argued that the populist right was not, as the narrative would have it, an unstoppable grassroots movement sweeping the world. Instead it should be seen as an outgrowth of the mainstream right, which fed it and gave it succour.

These colourful images are deeply misleading. Mr Farage did not bring about the Brexit vote all by himself. He needed two mainstream Conservative politicians, Boris Johnson and Michael Gove. More important still, the Leave vote was not just the result of spontaneous anti-establishment feelings by the downtrodden; Euroscepticism, once a fringe position among Conservatives, had been nourished for decades by tabloid newspapers and rebel MPs.

President Trump did not win as an outside candidate of a third-party populist movement either. Where Mr Farage had Messrs Johnson and Gove, Mr Trump could rely on the blessing of establishment Republicans such as Newt Gingrich, Chris Christie and Rudy Giuliani."

This is unarguably true in the case of Milo Yiannopoulos: he started his career at the Telegraph, once the newspaper of choice for retired colonels eating marmalade in the shires. Iain Martin, a colleague of his there, yesterday jokingly acknowledged that he was "partly to blame".

A quick look at Nigel Farage's experience during the EU referendum is also instructive. The Vote Leave campaign worked hard to shut him out of the public discussion in the weeks before 23 June - reasoning that his overt anti-immigration broadsides would turn off swing voters. They even accused broadcasters of "joining the IN campaign" by inviting Farage to debate David Cameron. To understand Farage's bewilderment at this treatment, read his speeches from the time, or his grumpy appearance on TV the morning after the victory, where he said the £350m NHS claim was a mistake. The guy felt betrayed.

And it's not surprising. A significant number of Tory Eurosceptics in parliament had, until Cameron announced the referendum would happen, found Farage's existence extremely useful. There he was - a living, breathing, chainsmoking reminder that MPs (and voters) could move to Ukip if Britain didn't get a say on membership of the European Union. But once the campaign began, they found him an embarrassment. The "Breaking Point" poster was repellent. He was turning off moderate voters. And so he was frozen out. Boris Johnson and Michael Gove suddenly discovered that - hey, this guy says some pretty outrageous things!

A similar dynamic happened with Donald Trump. We now know he performed on 8 November about as well as a generic Republican after eight years of a Democratic president. Certainly no better - had he run as an independent, that small core of Trump-lovers would be a speck within a wider population, instead of being held up as the vanguard of a new kind of politics. Throughout the campaign, GOP grandees like Paul Ryan struggled to condemn him, reasoning that a Republican president - any Republican president, even one who didn't seem to believe in most of the alleged values of the Republican party - was better than a Democrat. Trump was boosted and bolstered by significant portions of the mainstream right, and even the centre: CNN employed his former campaign manager as a pundit. Fox, a mainstream news channel owned by a huge corporation, gave him waves of adoring coverage.

***

What's in all this for the mainstream right? Two things. The first is that the populist right are useful generators of heat. They say outrageous things - black people are lazy! Muslims are terrorists! - putting their opponents in a bind. Do you let such assertions go, on the basis that those voicing them are a tiny fringe? Or do you wearily condemn every single instance of bigotry, making yourself look like a dull Pez dispenser of condemnation? Either way is debilitating, either for public discourse broadly, or for the left's appeal to disengaged people.

Secondly, the populist right are useful outriders. Sheltered by the mainstream right - would anyone read Katie Hopkins if she had a blog, or Piers Morgan? nope - these "provocateurs" can push extreme versions of narratives that many on the mainstream right feel to be true, or at least to contain a kernel of truth worth discussing. If Breitbart says "black crime" is a distinct phenomenon, then it's much more acceptable for Trump to threaten to "send in the Feds" to Chicago, or to describe inner cities as wastelands in need of a strong hand. If Katie Hopkins writes about migrants drowning in the Mediterranean as "cockroaches", she dehumanises them - turning them from fathers, mothers, children into a faceless mass, not like us, and therefore not deserving of our pity. That makes it much easier for the government to stop taking child refugees. After all, didn't I read somewhere that they're all 45 and just pretending to be children, anyway?

The populist right are extremely good generators of memes - those little bits of information which move virally through society. Take the grooming gang in Rochdale. It gets invoked every time feminists try to have a conversation about male violence. Um, did you condemn Rochdale? By the time you reply, wearily, that yes you did, it's too late. The conversation has been derailed for good. What about FGM? Well, yes, of course I'm agains-- oh, too late. We've moved on.

***

The "alt right" - the online version of the populist right - loves to talk about left-wingers being "triggered" or "snowflakes". This is clearly a rhetorical tactic to delegitimise any criticism of them. I don't write about misogyny because I'm upset by it; I write about it because it's wrong. But it's a playbook that works: look into examples of "political correctness gone mad" and you'll often find a story that has been exaggerated, twisted or straight-up invented in order to paint the left as dolorous monks intent on killing fun. But anyone with any strong beliefs, anyone who holds anything sacred, will react when some shows disrespect to something they care about. The right has just as many shibboleths it is unwilling to see violated. (If you don't believe me, try burning a poppy or the American flag.)

The strangest part of yesterday was seeing Milo Yiannopoulous's increasingly sincere Facebook posts, as the awful realisation dawned on him - as it dawned on Nigel Farage during the referendum - that the sweet shelter of the mainstream right was being withdrawn from him. When he had attacked his female peers in the London tech scene, when he attacked transgender people for being "mentally ill", when he attacked an actor for the temerity to be black, female and funny in a jumpsuit, he was given licence. He was provocative, starting a debate, exercising his free speech. But yesterday he found out that there is always a line. For the right, it's child abuse - because children, uniquely among people who might be sexually abused, are deemed to be innocent. No one is going to buy that a 13-year-old shouldn't have been out that late, or wearing that, or brought it on himself.

I would not be surprised if this isn't the end of Milo Yiannopoulos's career, and I will watch with keen interest what strategies he will use for his rehabilitation. He's still got his outlaw cachet, and there are still plenty of outlets where the very fact that people are objecting to a speaker is assumed to mean they have something that's worth hearing. And there are plenty more ideas that some on the right would be happy to see pushed a little further into the mainstream - with plausible deniability, of course. If that's the extreme, then the mainstream shifts imperceptibly with every new provocation. Because he's not one of us, oh no. They're not, either. But you see, they must be heard. And provocateurs are useful, until they're not. But it's not the left who decides when that is. Only the mainstream right can stop the extremists on their flanks.