I'm going to be straight forward: don't read this book if you don't have a particular interest in the history of ideas or intellectual history of the mid-20th century. Because this book is largely marked by the period in which it was written, around 1954-55, during the height of the Cold War. Raymond Aron (1905-1983) was still a rising French intellectual, did not yet have a permanent position at a university or a research institution, but had already made himself noticed in the polemic surrounding Marxism and more specifically Stalinism, especially because he undisguisedly opposed what he called the idolatry of extreme left-wing ideas. In this book he systematically explains his views on this. In other words, you must have some knowledge of Marxism itself, and especially of the French intellectual landscape of the 1950s. And – with my apologies – still 1 element that makes the reading difficult: the book is not as homogeneous as I expected, sometimes it looks more like a collection of previously published articles. (By the way: I read this in French, so I couldn’t comment on the translation)

Enough warnings. What I especially want to emphasize is how lucid Aron's analyzes were: how fearlessly he attacked all the sacred cows (in this case of the left), in an argument that razor sharply exposed the contradictions of Marxism and especially Stalinism and de facto proved how those views in reality were wrong. But there's more. Aron frames his judgment in a broader vision of the naive progressive optimism of the left, of exaggerated philosophies of history in Western culture, of the idolization of the phenomenon of 'revolution' in France, and of the own moral psychology of the intellectual elite. With regard to the latter, in my opinion he occasionally went a bit out of line, for example by scornfully pointing out that intellectuals are not insensitive to the 'pecuniary aspects' of the public forum.
I could write endless more about this book, but others have done it much better. I conclude by underlining that - although this book is very dated, especially in terms of context - it is nevertheless testimony to a lucid and brilliant mind, whose right has been confirmed by history.
In my History account on Goodreads I go into a little more detail about Aron's philosophy of history: https://www.goodreads.com/review/show/6046153633. ( )

Raymond Aron's masterpiece, "The Opium of the Intellectuals", uses Marx' famous description of the nature of religion to turn it against the latter-day followers of Marxism in France, in particular the Stalinist fellow travellers of the 1950s and their "Third Way"-ish epigones of the 1960s. Against these, Aron flings volley after volley of critique, most of it aimed to demonstrate the debatability if not meaninglessness of the concepts used by these authors (Sartre, Merleau-Ponty, etc.), such as "The Proletariat", "The Revolution", "The Meaning of History", and so on and so forth. Aron's criticisms of the many-sidedness, flexibility and reified nature (if we may use that Marxist term here) of those terms is well-done and in most cases hits home.

Less certain is Aron's general criticism of the French left and its intellectual pretensions. The more Aron leaves the easily attacked Stalinists for what they are and the more he tries to attack the general viewpoint of leftist politics, whether communist or not, the more vague and meandering his arguments get and the less clear his actual point becomes. He seems to be leaning on a Weberian idea of responsibility in politics, involving the need to deal mainly with practical and administrative problems rather than invoking grand phrases, and he also has some discussions about the importance of "productivity" and how considerations of this inevitably have to govern the real political debates of the kind he feels are sensible. But what he means by this "productivity" is never explained, and his side discussion about philosophy of history only makes this more confused.

On the whole, Aron seems to be advocating a conservative and pragmatic approach to political issues, focusing on the need for making choices, dealing with practical problems, and compromise, something on the continent definitely belonging to the political center-right. That Marxism-Leninism has mostly been ideological, uninterested in reality and full of hollow invective is certainly true, but even then it was no longer necessary for Aron to point it out - it was obvious to all but the orthodox communists themselves, and the famous collection "The God That Failed" had already been written, the XXnd Party Congress held. Almost nothing Aron writes in this book is applicable to the left in general, and in so far as he makes meaningful commentary about that, it is definitely incorrect; as can be seen from his general complete ignorance of economics (hidden behind a lot of vague phrasing), his Anglophilia, and his disinclination to understand socialism as anything else than state ownership of certain factories and the like.

That makes this work vaguely useful as a critique of the fashionable Leninism of the French left, and maybe also interesting as a document from the debates of those times, but it is of no lasting meaning or value.