I don’t have much to add, but what I do follows on from Norm’s comment that Hari “simply repeats the falsehood that the Euston Manifesto is a document of 'the pro-war left'. This has been answered many times… Perhaps the best-known signatory of the manifesto was Michael Walzer, and he opposed the war.”
This is quite true; indeed the EM specifically states that its signatories hold differing views on the Iraq war. But, aside from the perhaps niche arguments about the EM, Hari makes an even more basic mistake in his opening sentence:
The pro-invasion left was always a small battallion, comprised almost entirely of journalists and intellectuals who believed toppling the Taliban and Saddam Hussein was a good idea - even if the only President available to lead the charge was George Bush.
There were certainly people on the left who thought toppling the Taliban was a good idea; there were people who thought toppling Saddam was a good idea; and there were people who thought toppling the Taliban and Saddam were two good ideas – but not that they were one single good idea.
A phrase like “the pro-invasion left” is meaningless without reference to a specific invasion. Would someone who supported Afghanistan but not Iraq count as a member? What about someone who opposed both, but supported Kosovo and would have supported Rwanda? What is the “pro-invasion left” position on Sudan, Zimbabwe, Iran, North Korea, Russia, China…?
The phrase is fatuous and facile, serving to conflate different opinions and turn a debate about policies to one about factions, so that Hari can damn Cohen and others as joined to a “neoconservative” crusade to further US oil interests under the guise of saving the world through force.
Another small point: those who were on the left and favoured invading Iraq were far more likely to be working class than members of the intelligentsia. But they tend not to write about it quite so much.