Julian Assange is wanted for crimes that put at risk the lives of people in Iraq, Iran and Afghanistan who had helped the west, some of whom later disappeared, said a lawyer acting for the United States in its bid to extradite him.
Almost a decade since his WikiLeaks website enraged Washington by leaking hundreds of thousands of secret US documents, Mr Assange, 48, is fighting extradition from Britain to the United States where he is accused of espionage and hacking.
James Lewis, lawyer for the US authorities, said Mr Assange was wanted not because he embarrassed the authorities but because he put informants, dissidents, and rights activists at risk of torture, abuse or death.
"What Mr Assange seems to defend by freedom of speech is not the publication of the classified materials but the publication of the names of the sources, the names of people who had put themselves at risk to assist the United States and its allies," Mr Lewis said at London's Woolwich Crown Court.
The United States asked Britain to extradite Mr Assange last year after he was pulled from the Ecuador embassy in London, where he had spent seven years holed up avoiding extradition to Sweden over sex-crime allegations which have since been dropped.
Mr Assange has served a prison sentence in Britain for skipping bail and remains jailed pending the US extradition request.
Mr Lewis, speaking on behalf of the US authorities, said hundreds of people across the world had to be warned after the WikiLeaks disclosures. Some had to be relocated. Others later disappeared, he said, although he said the United States would not try to prove that was directly a result of the disclosures.
The United States has charged Mr Assange with 18 criminal counts of conspiring to hack government computers and violating an espionage law.
Supporters hail Mr Assange as an anti-establishment hero who revealed governments' abuses of power, and argue the action against him is a dangerous infringement of journalists' rights.
Chants from his backers outside could be clearly heard in court. Mr Assange himself complained about the din.
"I'm finding it difficult concentrating," said Mr Assagne. Judge Vanessa Baraitser warned those in the public gallery not to disturb the proceedings.
Mr Assange's lawyer said he should not be extradited as he would not get a fair trial and would be a suicide risk.
Lawyer Edward Fitzgerald said that the US attitude to Mr Assange had changed when US President Donald Trump came to power and that the US president wanted to make an example of his client.
He said that in 2013 the US government, under former president Barack Obama, had decided that Mr Assange should not face any action. But that in 2017, after the 2016 election of Mr Trump, an indictment was brought against Mr Assange.
Why the change, asked Mr Fitzgerald. "The answer is President Trump came into power with a new approach to freedom of speech and a new hostility to the press amounting effectively to declaring war on investigative journalists," Mr Fitzgerald said.
All claims against Assange are fraudulent, says father
Mr Assange's father has agreed that his son will exhaust all avenues to prevent extradition to the US.
Speaking on RTÉ's Drivetime, John Shipton said that his son "is innocent and that all claims against him are fraudulent".
He said his son's imprisonment conditions have improved and he visits him regularly now.
He said he had spent 22-23 hours a day in his cell in Istanbul, where he said protocol stated that he needed to be in solitary confinement.
Mr Shipton said restriction to his papers and lawyers made his son's life more uncomfortable.
Yesterday, Mr Shipton claimed his son had been "harassed" by a prison cell search.
Mr Shipton criticised the "plague of malice", which he said "emanates from the Crown Prosecution Service" towards Mr Assange.
He urged that his son be allowed bail, telling reporters: "For the life of me I can't understand why Julian Assange is in jail having committed no crime, with family here that he can come and live with."
Mr Varoufakis said Mr Assange was in a "very dark place" due to spending more than 20 hours a day in solitary confinement.
He called for the extradition to be stopped "in the interests of 300 years of modernity, 300 years of trying to establish human rights and civil liberties in the west and around the world".
More than 40 international legal experts have written to British Prime Minister Boris Johnson demanding the "rule of law be upheld", claiming he has not had proper access to his legal team.
The letter was handed in to 10 Downing Street on Saturday and also urged the British legal community to act "urgently" to secure Mr Assange's release.
Mr Assange has been held on remand in Belmarsh prison since last September after serving a 50-week jail sentence for breaching his bail conditions while he was in the Ecuadorian embassy in London.
Additional reporting AFP