By the time the second plane hit the World Trade Centre, the battle to define the 9/11 attacks had already begun, on both sides of the Atlantic. In the US President Bush made the fateful call for a war on terror, as the media rallied to the flag. In Britain Tony Blair and his cheerleaders enthusiastically fell into line. Inevitably, they faced a bit more opposition to the absurd claim that the atrocities had come out of a clear blue sky, and the country must follow wherever the wounded hyperpower led.

But not a lot. Political and media reaction to anyone who linked what had happened in New York and Washington to US and western intervention in the Muslim world, or challenged the drive to war, was savage.

From September 11 2001 onwards, the Guardian (almost uniquely in the British press) nevertheless ensured that those voices would be unmistakably heard in a full-spectrum debate about why the attacks had taken place and how the US and wider western world should respond.

The backlash verged on the deranged. Bizarre as it seems a decade on, the fact that the Guardian allowed writers to connect the attacks with US policy in the rest of the world was treated as treasonous in its supposed "anti-Americanism".

Michael Gove, now a Conservative cabinet minister, wrote in the Times that the Guardian had become a "Prada-Meinhof gang" of "fifth columnists". The novelist Robert Harris, then still a Blair intimate, denounced us for hosting a "babble of idiots" unable to grasp that the world was now in a reprise of the war against Hitler.

The Telegraph ran a regular "useful idiots" column targeted at the Guardian, while Andrew Neil declared the newspaper should be renamed the "Daily Terrorist" and the Sun's Richard Littlejohn lambasted us as the "anti-American propagandists of the fascist left press".

Not that the Guardian published only articles joining the dots to US imperial policy or opposing the US-British onslaught on Afghanistan. Far from it: in first few days we ran pieces from James Rubin, a Clinton administration assistant secretary; the ex-Nato commander Wesley Clark; William Shawcross ("We are all Americans now"); and the Washington Post columnist Jim Hoagland, calling for vengeance – among others backing military retaliation.

The problem for the Guardian's critics was that we also gave space to those who were against it and realised the war on terror would fail, bringing horror and bloodshed to millions in the process. Its comment pages hosted the full range of views the bulk of the media blanked; in other words, the paper gave rein to the pluralism that most media gatekeepers claim to favour in principle, but struggle to put into practice. And we commissioned Arabs and Muslims, Afghans and Iraqis, routinely shut out of the western media.

So on the day after 9/11, the Guardian published the then Labour MP George Galloway on "reaping the whirlwind" of the US's global role. Then the Arab writer Rana Kabbani warned that only a change of policy towards the rest of the world would bring Americans security (for which she was grotesquely denounced as a "terror tart" by the US journalist Greg Palast). The following day Jonathan Steele predicted (against the received wisdom of the time) that the US and its allies would fail to subdue Afghanistan.

Who would argue with that today, as the US death toll in Afghanistan reached a new peak in August? Or with those who warned of the dangers of ripping up civil rights, now we know about Guantánamo, Abu Ghraib and "extraordinary rendition"? Or that the war on terror would fuel and spread terrorism, including in Pakistan, or that an invasion of Iraq would be a blood-drenched disaster – as a string of Guardian writers did in the tense weeks after 9/11?

As the Guardian's comment editor at the time, my column in the immediate aftermath of 9/11 was a particular target of hostility, especially among those who insisted the attacks had nothing to do with US intervention, or its support for occupation and dictatorship, in the Arab and Muslim world. Others felt it was too early to speak about such things when Americans had suffered horrific losses.

But it was precisely in those first days, when the US administration was setting a course for catastrophe, that it was most urgent to rebut Bush and Blair's mendacious spin that this was an attack on "freedom" and our "way of life" – and nothing to do with what the US (and Britain) had imposed on the Middle East and elsewhere. And most of the 5,000 emails I received in response, including from US readers, agreed with that argument.

Three months later Kabul had fallen, and Downing Street issued a triumphant condemnation of those in the media who had opposed the invasion of Afghanistan (including myself and other Guardian writers) and had supposedly "proved to be wrong" about the war on terror. Rupert Murdoch's Sun duly denounced us as "war weasels".

Among these "weasels" was the Guardian's Madeleine Bunting, who had raised the prospect that Afghanistan could become another Vietnam and the focus of "protracted guerrilla warfare" – when the former Liberal Democrat leader Paddy Ashdown (like the government) was insisting that the idea of a "long drawn-out guerrilla campaign" in Afghanistan was "fanciful". A decade on, we know who "proved to be wrong".

The most heartening response to the breadth of Guardian commentary after 9/11 came from the US itself, where debate about what had happened, and why, was as good as shut down in the mainstream media in the wake of the attacks. One byproduct of that official public silence was a dramatic increase in US readership of the Guardian's website, as millions of Americans looked for a perspective and range of views they weren't getting at home.

Traffic on the Guardian's website doubled in the months after 9/11, driven from the US. Articles from the Guardian were taped in bookshop windows from Brooklyn to San Francisco. As Emily Bell, then editor of Guardian Unlimited and now digital director at Columbia's Graduate School of Journalism, puts it, the post-9/11 debate was "totally transformative" for the Guardian, turning it into one of the two fastest growing news sites in the US – and creating the springboard for a US readership now larger by some measures than in Britain.

Which only goes to show how those who accused us of "anti-Americanism" in 2001 so utterly misjudged the society they claimed to champion.