Matthew Prince had the power to kill the white supremacist hate site the Daily Stormer for years, but he didn’t choose to pull the trigger until 16 August. That’s when the chief executive of website security company Cloudflare “woke up … in a bad mood and decided to kick them off the Internet”, as he told his employees in an internal email. Without Cloudflare’s protection, the Daily Stormer was forced to retreat to the darknet, where it is inaccessible to the majority of internet users.

Cloudflare is just one of many internet companies that cleaned house amid a wave of public outrage following a deadly white supremacist rally in Charlottesville. Critics charge that technology platforms have enabled a disparate network of racist extremists to seek one another out, raise funds, and plan and execute such rallies. But unlike consumer facing companies such as Facebook, YouTube, PayPal and Discord, and even as liberal voices – including the Guardian editorial board – applaud it, Cloudflare won’t defend its actions.

“I am deeply uncomfortable with the decision we made,” Prince said in an interview. “It doesn’t align with our principles.”

The primary principle at stake – that the US and the internet both remain free speech zones, even for Nazis – has never been more fraught.

“This is a really terrible time to be a free speech advocate,” said Jillian York, director for international freedom of expression at the Electronic Frontier Foundation. “It’s a ‘First they came for the … situation,” she said, referring to the famous Martin Niemöller poem about the classes of people targeted by Nazis, “only in reverse”. York said that it was frustrating that the debate around online censorship was gaining traction when it impacted neo-Nazis, rather than the other classes of people who have been harmed by it for years, including breastfeeding mothers, artists, and transgender activists.

Though these are dark days for American exceptionalism, the US remains distinct in its commitment to freedom of speech. Even as many Americans increasingly favor European-style limitations on hate speech, the constitution’s first amendment ensures that any such legislative effort is likely a non-starter.

But the fate of the Daily Stormer – as vile a publication as it is – may be a warning to Americans that the first amendment is increasingly irrelevant.

“Historically, the place you went to exercise your speech rights was the public square. Now the equivalent is Twitter and YouTube and Facebook,” said Daphne Keller of the Stanford Center for Internet and Society. “In a practical matter, how much you can speak is not in the hands of the constitution but in the hands of these private companies.”

The idea of social media platforms as the “modern public square” was recently endorsed by the US supreme court, which ruled unanimously that barring sex offenders from Facebook and Twitter violated their first amendment rights.

And yet, this digital version of the public square is more closely analogous to “privately owned public spaces” – a very American type of park whose legal particularities became widely known in 2011 when the Occupy Wall Street movement set up camp in one such space.

The 'alt-right' now resemble the evicted Occupiers, standing outside a sanitized space in which they once thrived

Manhattan’s Zuccotti Park seemed like the quintessential free speech public square when it became ground zero for a movement built around general assemblies, speaker stacks, and the “people’s mic”. But the public-private nature of the space was built into the movement’s rise and eventual fall: the encampment was only possible in the first place because the privately owned space remained open 24 hours a day, unlike truly public parks, which close at night. And the ability of plaza’s commercial real estate owners to unilaterally change the park’s rules facilitated the protest group’s eventual eviction.

As opposite as their politics may be, members of the so-called “alt-right” now find themselves in a similar position to the evicted Occupiers when it comes to the internet platforms where they once thrived: standing outside the gates while power washers sanitize the park for the use of others.

Quick Guide What is the 'alt-right'? Show Who coined the term 'alt-right'? The white supremacist Richard Spencer devised the term in 2010. He has described the movement as "identity politics for white Americans and for Europeans around the world". What does it stand for? The movement supports extreme rightwing ideologies, including white nationalism – used interchangeably with white supremacism – and antisemitism. It positions itself broadly against egalitarianism, democracy, universalism and multiculturalism. Some "alt-right" supporters have argued that their hardline, extremist positions are not truly meant, but are a way to disrupt conventional and accepted thinking. Memes, irony and ambiguity are sometimes used in an attempt to wrongfoot critics. How does the 'alt-right' relate to the Trump administration? The Trump administration includes figures who are associated with the "alt-right", including the former Breitbart News executive chairman Steve Bannon, who worked as chief strategist in Trump's White House in 2017. Many of Trump's policy positions have won favour with the movement.

American technology companies that were once imbued with the ethos of Twitter’s famous sobriquet – “the free speech wing of the free speech party” – have changed the rules, or at least decided to start selectively enforcing rules that are technologically unfeasible to apply across the board.

This crackdown means that our public square might as well be in Brussels. Pressure from the European Union moved Facebook, Twitter, YouTube and Microsoft in 2016 to adopt a hate speech “code of conduct” that is much more stringent than what US law would require, Keller said. And even without the influence of the EU, the industry’s reliance on advertisers produces its own incentives toward censoriousness.

Tech companies such as Twitter, once a free speech free-for-all, have begun changing the rules about who can say what. Photograph: Bloomberg/Bloomberg via Getty Images

“If you think of the 10 companies that have the infrastructure to really survive on the crazy dangerous internet that is out there, a huge percentage of them are advertising-driven companies,” said Prince. “They will by their very nature have a much more filtered, cleaned up version of the internet because that is where their economic incentives are.”

The overwhelming dominance of cyberspace by those handful of companies means that the battle over speech that is protected by the first amendment, rather than corporate terms of service, will be relegated to the remaining, truly public spaces in the real world, such as the public university campuses that have become the forum of choice for rightwing provocateurs like internet troll Milo Yiannopoulos and white nationalist Richard Spencer.

At certain points in US history, an embrace of free speech was a liberal’s rhetorical trump card. But amid the political turbulence of 2017, members of the #resistance have cheered the internet crackdown on the far-right and called for the exclusion of rightwing extremists to assemble in public spaces, from Boston to San Francisco. Meanwhile, supporters of a president who routinely rails against the free press have enthusiastically donned the mantle of first amendment freedom fighters.

“We are the new free speech movement,” declared the Berkeley College Republicans this spring, as they fought for the right to host Yiannopoulos on campus. “The Free Speech Tech revolution has begun,” announced social media startup Gab, which positions itself as a free-speech alternative to Twitter and Facebook but is largely populated by rightwing exiles of the major social networks.

Gab CEO Andrew Torba declined to be interviewed by the Guardian, which he called “very fake news”.

If the left does abandon its free speech principles, it may come to regret it.

“I’m really surprised to see liberals talk about what speech needs to be taken down, and not take that conversation a step further and talk about who is actually doing the censoring,” York said, questioning whether we should trust either the government or “unelected white Silicon Valley dudes” to make such decisions.

Or as Keller says: “We should not expect the new speech gatekeepers to be benign forever, or to enforce rules that we agree with forever.”