It is now approaching 20 years since the left — the classic, revolutionary, Marx- and Lenin-inspired left — received its death blow. Since 1989, not even those who look back lovingly at 1917, the year of the Bolshevik Revolution, and 1871, the year of the Paris Commune, have really believed that they would see such utopian experiments repeated. This was an especially debilitating blow to the Marxist tradition, whose major premise was that revolution is not simply desirable, but inevitable: that History, driven by its inherent contradictions, would necessarily move toward a climactic catastrophe, after which plenty and justice would reign forever. If History was clearly moving in the opposite direction — if capitalism was producing plenty and justice, while communism produced only oppression and poverty — then what remained to make the left the left?

In his new volume, “Left in Dark Times” (Random House, 256 pages, $25), the French intellectual Bernard-Henri Lévy gives a convincing and very troubling answer to that question. Gone, he writes, are the left’s inspiring and necessary ideals: its universalism, its love of justice, its sympathy with the oppressed, its commitment to truth-telling. In their place is a toxic brew of hatreds: of America, conceived as the imperial culprit behind all the world’s crimes; of Israel and the Jews, who now occupy the same place in the left’s demonology that they once held for the nationalist right; even of liberalism itself. Mr. Lévy compares the left — especially, but not exclusively, the French left — to a decomposing body, whose process of decay is releasing noxious pathogens. “Some weak notions,” he writes, “derive a potent energy from their very weakness; some are like bad cells in a body that phagocyte the good ones, killing them but taking nourishment from them.”

Mr. Lévy’s critique is all the more credible because he is himself a man of the left, and proud of the fact. He opens “Left in Dark Times” with a vignette of his telephone conversation with President Sarkozy, during the latter’s 2007 election campaign. Mr. Lévy was a friend and admirer of Mr. Sarkozy’s, yet he could not bring himself to vote for the conservative candidate. “Why didn’t I vote for Sarkozy?” he asks at the beginning of the book. “Why was I so profoundly convinced, then, that it was literally impossible for me to vote for that man?” The reason, he explains, is that his heart and his identity belong irretrievably to the left, to the Socialist Party. “No matter how much I like and respect you,” he told Mr. Sarkozy, “the Left is my family.”

Mr. Lévy’s decision to start the book with this story tells us a great deal about the man. He brags of his closeness to power, the way he can get the president of France on the phone, and also of his celebrity, which makes him such a valuable asset to a political campaign. (In the end, he worked actively for Mr. Sarkozy’s defeated rival, Ségolène Royal.) Later in the book, he will write with serene immodesty about his exploits in Portugal, where he witnessed the overthrow of the Salazar dictatorship, and Bangladesh, where he covered the war between India and Pakistan. In short, he is always conscious that he is not just an intellectual but a brand — BHL, with his good looks and open shirts and actress wife and inherited fortune.

Mr. Lévy’s prose, too, seems to wear an open shirt. In “Left in Dark Times,” he writes very casually, with a rhetorical heat and rhythm better suited to the platform than the page. The book is full of one-sentence paragraphs, run-on sentences, and repetitions. Nor does he shy away from garishness and grandiosity. “Still later, in Italy,” runs one nostalgic passage, “the university amphitheaters filled to overflowing, overheated, wherever I came … Bologna. Milan. Shouts. Raised fists. Terrible, exalted condemnations. Embittered fervor.” Glory days!

This is not how intellectuals write, or act, in America, and it gives “Left in Dark Times” an odor of frivolity. Yet Mr. Lévy is far from a frivolous thinker. He came to prominence in the 1970s as part of the so-called new philosophy movement, whose newness was precisely its rejection of the old communist verities. One of his most famous books described Marxism as “barbarism with a human face.” In his new book, he writes scathingly of “the totalitarian temptation” of which the left was guilty: “the notion that revolution isn’t a fancy-dress party and that because it’s a revolution it’s worth a few mass graves beneath the sun of Good, for the sake of the New Man; the fascination of the clean slate and the white page, which until my generation drove so many projects and desires; the profane millenarianism that was, until so recently, the religion of progressive humanity and whose principal article of faith could be summed up, in its popular version, in the famous saying ‘You can’t make an omelet without breaking a few eggs.'”

Yet as he goes on to write, “all of that, as everyone knows, isn’t exactly the problem today.” The left has neither the ideological fervor nor the political strength to make a revolution anywhere in the West. Mr. Lévy’s key point, however, is that this weakness does not equal harmlessness. The left may be “hanging between two worlds, smoke without fire … words without meaning, leaving the twentieth century without quite entering the twenty-first.” But its powerlessness has made it a prey to nihilism and despair, to the point that some of the most inhumane and undemocratic forces on the intellectual scene now march under the banner of the left.

The heart of Mr. Lévy’s book is his strong denunciation of those forces. There is, first of all, the left’s hatred of liberalism — the idea and the very word, which is anathema in French politics. This looks paradoxical to Americans, who are used to associating the word “liberal” with the left wing of the Democratic Party. But in Europe, liberal still carries its original 19th-century meaning as the philosophy of individual freedom; and this freedom, to the French left, is nothing but the Trojan horse of an all-devouring capitalism.

The left’s willingness to abandon the name and tradition of liberalism, to Mr. Lévy, is an ominous sign. “These morons,” as he calls them, forget that “the beautiful word liberty” was the original inspiration for the French Revolution, and for all truly emancipatory politics. Hating liberalism, he argues, means hating the Enlightenment. That is why the left, which once looked up to Lafayette, Locke, and Voltaire, can now flock to politicians such as the dictator Hugo Chavez of Venezuela, and even admire the Nazi philosopher Carl Schmitt.

Such a “Red-Brown” synthesis, Mr. Lévy writes, is only possible because the driving passion of today’s left is no longer liberty or even equality, but hatred. It is locked in a conspiratorial mind-set, which holds that since American capitalism is the root of all evil, all opponents of America or capitalism are ipso facto virtuous. That is why people who call themselves leftists have been found, over the last decade, supporting the genocidal regime of Slobodan Milosevic; and sympathizing with the fascist dictatorship of Saddam Hussein; and turning the 2001 Durban Conference against racism into a festival of anti-Semitic hatred; and deliberately ignoring the genocide in Darfur, because it doesn’t fit neatly into the anti-American worldview.

Mr. Lévy offers the best summary I have seen of that worldview, which can be glimpsed in the works of many influential left-wing philosophers and journalists. “We are in a world in which, on the one hand, we have the United States, its English poodle, its Israeli lackey — a three-headed gorgon that commits all the sins in the world — and, on the other side, all those who, no matter what their crimes, their ideology, their treatment of their own minorities, their internal policies, their anti-Semitism and their racism, their disdain for women and homosexuals, their lack of press freedom and of any freedom whatsoever, are challenging the former.” After reading “Left in Dark Times,” it is impossible to deny that the left, whatever its past glories — and Mr. Lévy remembers them all, from the Dreyfus affair to the events of 1968 — is now a danger to truly liberal values. A danger, despite its decrepitude: for as Mr. Lévy says, “even when they’re not in charge of anything, ideas are what, for better or worse, drive, and allow us to change, the world.”

akirsch@nysun.com