“Oh yeah, look at those dead bastards,” and “ha, ha, I hit them” say the pilots of a US Apache helicopter in jubilant conversation as they machine-gun Iraqi civilians on the ground in Baghdad on 12 July 2007.

A wounded man, believed to be the Reuters photographer, 22-year-old Namir Noor-Eldeen, crawls towards a van. “Come on buddy, all you have to do is pick up a weapon,” says one of the helicopter crew, eager to resume the attack. A hellfire missile is fired and a pilot says: “Look at that bitch go!” The photographer and his driver are killed.

Later the helicopter crew are told over the radio that they have killed 11 Iraqis and a small child has been injured. “Well, it’s their fault for bringing their kids into battle,” comments somebody about the carnage below.

Except there was no “battle” and all those who died were civilians, though the Pentagon claimed they were gunmen. The trigger-happy pilots had apparently mistaken a camera for a rocket propelled grenade launcher. Journalists in Baghdad, including myself, were from the start sceptical about the official US story because insurgents with weapons in their hands were unlikely to be standing chatting to each other in the street with an American helicopter overhead. As on many similar occasions in Iraq, our doubts were strong but we could not prove that the civilians had not been carrying weapons in the face of categorical denials from the US Department of Defence.

It was known that a video of the killings taken from the helicopter existed, but the Pentagon refused to release it under the Freedom of Information Act. Plenty of people were being killed all over Iraq at the time and the incident would soon have been forgotten, except by the families of the dead, if a US soldier called Chelsea Manning had not handed over a copy of the official video to WikiLeaks which published it in 2010.

The exposure of the Baghdad helicopter killings was the first of many revelations which explain why Julian Assange has been pursued for so long by the US and British governments. The claim by Theresa May echoed by other ministers that “in the United Kingdom, no one is above the law” is clearly an evasion of the real reasons why such efforts have been made to detain him on both sides of the Atlantic.

Jeremy Corbyn is correct to say that the affair is all about “the extradition of Julian Assange to the US for exposing evidence of atrocities in Iraq and Afghanistan.” But, within hours of Assange’s detention, it was clear that nobody much cared about innocent people dying in the streets of Baghdad or in the villages of Afghanistan and Assange has already become a political weapon in the poisonous political confrontation over Brexit with Corbyn’s support for Assange enabling Conservatives to claim that he is a security risk.

Lost in this dog-fight is what Assange and WikiLeaks really achieved and why it was of great importance in establishing the truth about wars being fought on our behalf in which hundreds of thousands of people have been killed.

This is what Daniel Ellsberg did when he released the Pentagon Papers about the US political and military involvement in Vietnam between 1945 and 1967. Like Assange, he exposed official lies and was accused of putting American lives in danger though his accusers were typically elusive about how this was done.

But unless the truth is told about the real nature of these wars then people outside the war zones will never understand why they go on so long and are never won. Governments routinely lie in wartime and it is essential to expose what they are really doing. I remember looking at pictures of craters as big as houses in an Afghan village where 147 people had died in 2009 and which the US defence secretary claimed had been caused by the Taliban throwing grenades. In one small area called Qayara outside Mosul in in 2016-17, the US air force admitted to killing one civilian but a meticulous examination of the facts by The New York Times showed that the real figure was 43 dead civilians including 19 men, eight women and 16 children aged 14 or under.

These are the sort of facts that the US and UK governments try to conceal and which Assange and WikiLeaks have repeatedly revealed. Readers should keep this in mind when they are told that Assange has narcissistic personality or was not treating his cat properly. If his personal vices were a hundred times more serious than alleged, would they really counterbalance – and perhaps even discredit – the monstrosities he sought to unmask?

The US government documents published by WikiLeaks are about the real workings of power. Take the Hillary Clinton emails published in 2016: much of the media attention has plugged into conspiracy theories about Russian involvement or, until the recent publication of the Mueller Report, the possible complicity of the Trump election campaign with the Russians. Many Democrats and anti-Trump journalists managed to persuade themselves that Assange had helped lose Hillary Clinton the election, though a glance at a history of the campaign showed that she was quite capable of doing this all by herself by not campaigning in toss-up states.

But look at what the emails tell us what the way the world really works. There is, for instance, a US State Department memo dated 17 August 2014 – just over a week after Isis had launched its offensive against the Kurds and Yazidis in Iraq that led to the butchery, rape and enslavement of so many.

It was a time when the US was adamantly denying that Saudi Arabia and Qatar had any connection with Isis and similar jihadi movements like al-Qaeda. But the leaked memo, which is drawn from “western intelligence, US intelligence and sources in the region” tells us that they really knew different. It says: “We need to use our diplomatic and more traditional intelligence assets to bring pressure on the governments of Qatar and Saudi Arabia, which are providing clandestine financial and logistic support to Isis and other radical groups in the region.”

This is important information about the level of priority the US gave to keeping in with its Saudi and Qatari allies while it was supposedly fighting the “war on terror”. This had been true since 9/11 and remains true today. But in much of the British media such issues are barely considered and the debate is focused firmly on the reasons why rape charges were not brought against Assange by Swedish courts and his culpability in taking refuge in the Ecuadorian embassy in London. Anybody who highlights the importance of the work which Assange and WikiLeaks has done is likely to be accused of being light-heartedly dismissive of the accusations of rape.

Assange is likely to pay a higher price than Ellsberg for his exposure of government secrets. The Pentagon Papers were published when the media was becoming freer across the world while now it is on the retreat as authoritarian governments replace democratic ones and democratic governments become more authoritarian.

The fate of Assange will be a good guide as to how far we are going down this road and the degree to which freedom of expression is threatened in Britain at a time of deepening political crisis.