HOW the mighty are falling. From Hollywood and Westminster to the City and now international aid charities, the walls of the citadels are cracking, old assumptions about power and its invulnerability turning to rubble.

Yet up on the hill, the shiny new builds that are the social media giants are safe from the tremors, their walls unscalable, their doors firmly barred to criticism. No one can touch this Google, this Facebook, this YouTube, this Twitter. Or at least no-one until now.

Keith Weed is the name and plain speaking is the game. Well, that and being the chief marketing officer for Unilever, makers of Persil, Ben & Jerry’s ice cream, Dove, Simple skin care, Marmite, Knorr products, and many another brand in the world’s cupboards. With a £6 billion budget, Mr Weed is the very model of a chief executive who speaks softly and carries a big stick.

The occasion was the Interactive Advertising Bureau conference in California, a get-together that usually only features in the trade press and the inside pages of the Financial Times. This time, however, the warning shot fired by Mr Weed was heard around the business world and wider.

“We cannot have an environment where our customers do not trust what they see online,” he said. Citing “fake news, racism, sexism, terrorists spreading messages of hate, toxic content directed at children” among the horrors lurking on the web, he said people were becoming increasingly concerned about the impact the digital world was having on “wellbeing, on democracy, and on truth itself”.

His message to the social media giants was clear: if you fail to protect children, if you promote anger and hate, if you create division in society, we will take our money elsewhere.

One industry executive has likened Mr Weed’s intervention to the launch of the #MeToo movement when the cyber tide turned in favour of those speaking out about sexual misconduct and against the perpetrators. If this is a tipping point, the social media behemoths can hardly say they were not warned it was approaching.

At the World Economic Forum in Davos in January, entrepreneur Marc Benioff compared the tech giants to the out of control banks that caused the financial crash of 2008. Prime ministers, including our own, and presidents have taken them to task. Parliamentary committees here and internationally. The European Commission. Prince William. Legions of users. Newspapers, broadcasters. All have tried to make their voices heard.

Even those who earned their billions from social media, including Sean Parker, Napster co-founder and former Facebook president, have spoken out about the ways firms hook users and keep them coming back for more. All these complaints, all this anger. There have been warm words, certainly. Promises to take on more staff to moderate content. Much muttering about changes to algorithms.

Yet still little to nothing has been done to clear the mountains of trash that have grown up around the edges of the web. Gaze on these for long enough and all matter of stomach-churning sights and vile opinions can be picked out. Day after day, terrorists and other hatemongers, peddlars of porn and suppliers of all sorts of under the counter commodities, continue to pour more material on. The stench is overpowering, the shadows cast are large and growing. Nothing and no-one can truly consider themselves safe from contamination, not children, not democracy.

As Keith Weed put it, parts of the internet we have ended up with are a million miles from where we thought it would take us. How did we get here? One could say that just as the internet shows the best of humanity - its ingenuity, generosity, capacity for kindness and fellow feeling - it features the worst, too. There was an open invitation to this party, remember, and everybody came. Was it not inevitable that a few wrong ‘uns would gatecrash the bash for their own ends? Why should tech giants be responsible for security on the doors now?

Well, for one, because they have profited so much from the lawlessness that has taken hold. By positioning themselves as “platforms” rather than traditional publishers, they have avoided being held to the same standards and laws as the rest of us in the information dissemination business. By accident or design they were allowed to do what they wanted, and they did. As the profits grew bigger a sense of entitlement set in. Ethics, tax, the laws of libel and copyright: they were for the little people. Social media was bigger than all that. It was too big to curtail.

But no longer if other firms follow the lead set by Unilever. There has been some debate within the industry as to how much of an impact one company can have, regardless of its size. Doubters will point to other boycotts which came to nothing once firms realised that Google and Facebook are the only game in town when it comes to reaching certain audiences. Others will see Unilever’s move as a way of driving down ad rates and in time making a very rich multinational (£113 billion and counting) even richer. Businesses are not charities, as Unilever showed recently when it announced the closure of its Colman’s Mustard factory in Norwich with the loss of 50 jobs.

Yet the firm’s intervention against the tech giants represents the best chance to date of turning social media around and making it a more responsible part of the society it claims to serve.

Social media firms have not cleaned up their acts so far because inaction has cost them nothing. Does anyone seriously believe that if social media firms were subject to the same laws, and fines, as other publishers that they would not have taken action before now? These firms have earned their billions by breaking technological barriers and fine tuning systems. They come down hard on anyone who does not abide by their rules. Yet policing their own content, playing fair by all, appears to be beyond them.

Sure, a few suits have appeared uncomfortable before legislators. The odd scratch and dent has surfaced on the firms’ reputations. But these are vague commodities that do not show up clearly in the accounts. The loss of billions in ad revenue will. When £6 billion talks, chief executives listen. Even the ones high on the hill.