It is easy to suspect that the web makes us stupid. I could fill the rest of this newspaper with anecdotes of British leftists using Facebook to reinforce each other’s belief that Corbyn’s leadership is a triumph; of cybernats turning to Twitter to bury the nagging feeling that an enormous deficit would have left an independent Scotland close to bankruptcy; or of American conservatives finding incontrovertible proof on white supremacist sites that President Obama is a Muslim.

As I only have this space, I will give you the story of Charlie Sykes. I don’t believe anyone can count themselves properly adult unless they stop at some point in their lives and think through every prejudice they hold. The US shock jock did so last week and confessed at the end of his self-examination to being frightened by the conservative movement he had helped nurture.

When Donald Trump told a lie, Sykes said, he could no longer say to his audience: “By the way, you know it’s false.” Facts were biased now. Fact-checkers were the hirelings of the hated liberal media. The fact was his fellow conservatives had had it with facts. The partisan web was their trusted source. If they’d read Trump was telling the truth on a conservative site or Facebook, that was all the confirmation they needed.

Sykes described an “alternative media reality and there’s no way to break through it. I swim upstream because, if I don’t say these things from some of these websites, then suddenly I have sold out. Then they will ask what’s wrong with me for not repeating these stories that I know not to be true.”

Suspecting the web has made us stupid is not the same as proving it, however. To understand is not to pardon, and I do not mean it as an exoneration when I say you can make a good argument that the populist movements sweeping the rich world are understandable reactions to modern crises and fears, not a by-product of new communications technology.

A minority of schoolchildren in the United States are white, and within 25 years whites will become a minority in the American population as a whole. You would be naive in the extreme not to have expected a frenzied backlash. Meanwhile, here in Europe, Marine le Pen and Nigel Farage haven’t come from cyberspace. Economic insecurity and mass migration are real, as is the murderous violence of the Islamo-fascists. The euro will truly never work. The banks really did collapse and governments really did fail to send bankers before judges, and compelled taxpayers to bail them out instead. All these things happened and would have changed politics whether Twitter existed or not. You do not appear to need technology to explain our discontents.

Facebook Twitter Pinterest Charlie Sykes, right, with Republican Ted Cruz. Photograph: Tannen Maury/EPA

Yet, listen to the jeering tone and cocksure ignorance of modern debate for a while, and think again. When Sykes talks about there being no way for the truth to break through alternative media reality, he is describing a world where people are so alienated from each other they cannot accept the good faith of an opponent who produces a discomforting argument. You can see the alienation in the T-shirts worn by Labour supporters announcing with pride that they’ve “never kissed a Tory”. They are not alone in their sexual taboos. In the 21st century, the idea of love crossing a political divide revolts partisans everywhere. In 1960 just 5% of Americans said they would be upset if their child married a supporter of a rival political party. By 2010, that number stood at 40%.

In a research paper published in the American Journal of Political Science, Yphtach Lelkes, Gaurav Sood and Shanto Iyengar found depressing proof that the web is fuelling segregation. The rollout of broadband in the US allowed them to conduct a controlled experiment. Access to new broadband services varied wildly because each state had different “rights of way” laws governing the use of the conduits, trenches and towers broadband providers need. The researchers matched the attitudes of those who did and did not have broadband with data on partisan hostility from studies of voters beliefs in the 2004 and 2008 presidential elections.

Greater use of the web ensured that an admirer of Jon Stewart would think that conservatives were not just mistaken but stupid, or a viewer of Fox News would work on the assumption that liberals were wicked. Both sides could dismiss uncomfortable facts as lies. Both sides allowed their politics to become so bound up with their identity, opposing arguments felt almost as if they were physical assaults. As the authors put it in a separate paper: “Partisans discriminate against opposing partisans to a degree that exceeds discrimination based on race.”

Broadband access was worth studying because the better your connection the longer you spend online. Optimists might have hoped we would take the opportunity of fast broadband to read more widely, and challenge more preconceptions. Not a bit of it. The better the access to the web many enjoyed, the more they clung to their own kind. The longer they stayed online, the more they turned for comfort to ideologues who shared their ideology. Most use broadband to access entertainment from pornography to Game of Thrones, of course – assuming that is a distinction with a difference. But you do not have to live deep in an ideological silo to be affected. One study of voting behaviour estimated that watching a mere four minutes of Fox News a week was enough to increase the odds of an American voting for a conservative candidate.

It is vulgar determinism to believe that changes in politics can be reduced to changes in technology. That does not mean they cannot accentuate pre-existing hatreds and help create new ones. As they do, we face a future of hostile tribes, screaming at each other in incomprehensible tongues; of peoples with battlefields aplenty but without common ground.

It need not be that way. An urgent, if undiscussed, reform is for governments to legislate to stop Facebook and others using their algorithms to deliver news users want to hear, rather than need to hear. More important would be a cultural reaction against the impoverishment so many supporters of the populist movements exhibit. Their inability to argue, their denial of hard evidence, their certainties, and their fanatical denunciations of sellouts, traitors and apostates speak of men and women whose souls have withered along with their minds.

They should be made to face their own inadequacies, and asked politely but repeatedly: who wants to live their life with only the echo of their own voice for company?