In an interview with weekly newspaper Die Zeit, he said: “The fact of the matter is, millions of people have been killed in vicious circumstances on a regular basis throughout history.”
Mr Hallam cited mass murders in the Congo by the Belgians as an example, saying: “The Belgians came to the Congo in the late 19th century and decimated it.”
In that context, he suggested, the Holocaust was “almost a normal event … just another f***ery in human history”.
The comments prompted a swift and stern rebuke from Extinction Rebellion’s German branch, which said: “We firmly distance ourselves from Roger Hallam’s belittling and relativising remarks on the Holocaust.
“Roger violates the principles of XR, who do not tolerate antisemitism, and is no longer welcome at XR Germany.”
The UK chapter of the environmental movement, which has staged campaigns of civil disobedience around the world, also “unreservedly” denounced its founder’s remarks and said he could face expulsion.
Mr Hallam’s comments were widely condemned in Germany and led his publisher in the country to withdraw his upcoming book.
Foreign minister Heiko Maas said the Nazis’ industrial-scale murder of Jews was “uniquely inhuman”, adding in a tweet: “We must always be aware of this to ensure: never again!”
Robert Habeck, joint leader of Germany’s Green Party, told the newspaper Bild that “there must be no place for antisemitism or downplaying of the Holocaust” and urged Extinction Rebellion to distance itself from its founder.
The publisher Ullstein said it had cancelled the publication of Mr Hallam’s book, Common Sense for the 21st Century, which had been due in German book shops on 26 November.
Mr Hallam had spoken to Die Ziet to promote the book and is said to have referenced the Holocaust “several times” during the interview. He told the publication he believed Germany’s attitude to the Holocaust was harmful.
“The extent of this trauma can paralyse,” he said. “That prevents you from learning.”
Extinction Rebellion UK said it “unreservedly denounces” its co-founder’s remarks, which it noted were “made in a personal capacity in relation to the recent launch of his book”.
In a statement, it added: “Jewish people and many others are deeply wounded by the comments today.
“Internal conversations have begun with the XR conflict team about how to manage the conflict process that will address this issue. We stand by restorative outcomes as preferable, although in some cases exclusion is necessary.
“We stand in solidarity with XR Germany, with Jewish communities, and with all those affected by the Holocaust, both in the past and in our times.”
Mr Hallam suggested his remarks had been taken out of context.
“I fully acknowledge the unimaginable suffering caused by the Nazi holocaust, that led to all of Europe saying ‘never again’,” he told the Daily Telegraph.
“But it is happening again, on a far greater scale, and in plain sight. The global north is pumping lethal levels of CO2 into the atmosphere and simultaneously erecting ever greater barriers to immigration, turning whole regions of the world into death zones.
“Let’s be clear: the real outrage is not to speak about the Holocaust, the real outrage is the complicity in the global holocaust that is already underway. We are allowing our governments to willingly, and in full knowledge of science, engage in the genocide of our young people.”
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