This post appears on The Guardian's "Comment is Free" site.
Nick Cohen's book What's Left? is not centrally about a pro-totalitarian and anti-American fringe. To those who have read the book, this ought to be a truism. One person who hasn't, the former Liberal MP Michael Meadowcroft, querulously maintained in a letter to The Observer that the anti-Americanism Cohen skewers is confined to a "tiny minority of those who seek alternative ways of achieving world peace from the appalling judgment that led to the invasion of Iraq".
Among respectful reviewers, Peter Oborne complains that Cohen's "thesis simply does not begin to apply to the decent and honourable left-wing men and women who opposed the war".
There are certainly memorable vignettes in the book about that part of the left that requires from its adherents self-abasement as well as the abnegation of critical faculties. Cohen has found the notorious pamphlet written by Eric Hobsbawm and Raymond Williams in support of Stalin's invasion of Finland. He gives a brief history of the Workers' Revolutionary Party under the leadership of the thuggish, bonehead rapist Gerry Healy. He recounts the libels perpetrated by an obscure far-left/libertarian sect against ITN journalists reporting honestly and accurately on the Bosnian war. But if you maintain that these are isolated cases confined to an ideological extreme, you miss Cohen's thesis.
In the last century, material betterment and the steady diminution of discrimination against blacks, women and homosexuals have advanced progressive goals. Much of the left has yet to come to terms with this achievement. At the extreme, some who were once thought of as being on the left have adopted the language and outlook of the right.
The alliance of Islamists and Leninists that makes up the Respect coalition is not a dalliance born of opportunism. It reflects an extraordinary process in which part of the left has ended up arguing for what by any objective standards are reactionary positions: promotion of religious obscurantism in place of secularism; segregation of the sexes at public events; abridgement of free speech in deference to the sensibilities of those who claim themselves victims of the phantasm of "Islamophobia"; and most pernicious, the resurrection in political debate of some highly traditional motifs of antisemitic conspiracy theory.
This is a bizarre ideological metamorphosis, all right; but it is rarely stated as such. And in a less bleakly comic - so more plausible - form, the assumptions of what counts as a progressive politics subtly shift.
Last week on this site Agnès Poirier eloquently recounted her reasons for pulling out of a conference, organised under the auspices of the London Mayor, on the theme of the "Clash of Civilisations". The conference was an obviously loaded and tendentious exposition of multiculturalism (though regrettably it wasn't quite as obvious in advance to me, so I accepted an invitation to speak at it).
Quite apart from the subject matter, it was unremarked upon, and to the organisers clearly unexceptionable, that segregated "prayer rooms" were among the facilities provided - under the patronage of a left-wing municipal politician. This is a type of politics that elevates the demands of group identities - or rather, lobbyists for them - over the notion of a common citizenship with equal rights under law. The blight of identity politics is now a commonplace feature of the left, well beyond the ranks of the supporters of George Galloway.
In foreign affairs, the principle of humanitarian intervention on behalf of captive peoples under despotism has been catastrophically compromised by the culpable failures of the Bush administration in the Iraq war. The near uniform response of liberals, however, has been to welcome the proposals of James Baker and Lee Hamilton's Iraq Study Group.
These can be summarised as aiming for a stable balance of power in the region through friendliness with Iraq's despotic neighbours. The failure of that sort of misnamed "realism" may be gauged from the fact that when Mr Baker pursued such a policy in government its embrace extended as far as Saddam Hussein himself.
The left, with few exceptions, seems not so much content as insouciant at the political damage sustained by an approach that in the 1990s rebuffed the genocidal aggression of Slobodan Milosevic, preserved Sierra Leone from the vicious rule of private armies, and overthrew theocratic barbarism in Afghanistan.
We on the left had, and retain, a responsibility to stand with those whose only plausible prospect of liberation is intervention by western democracies. That responsibility is not, and never has been, adequately discharged by the solipsistic insistence that the cause of regime change is "not in my name".
Liberal interventionism is not a "trick", as Edward Pearce - voluble campaigner against the reversal of Saddam's annexation of Kuwait in 1990-91 - writes. It was an ideological mainstay of British social democracy and American liberalism in the late 1940s, when President Truman declared that "totalitarian regimes imposed on free peoples, by direct or indirect aggression, undermine the foundations of international peace and hence the security of the United States".
Isolationists of both wings of politics have never understood this connection. Autocracies seek enemies, as their own justification for existence. A better left would accept that role, if not with a portentous sense of historical obligation then at least with relish.
Nick Cohen's book (disclosure: the author is a friend, and I appear in the acknowledgements) has an exotic cast of characters. But, reader, it is also about you.