In the 1960s, as an undergraduate and eventually a graduate student in philosophy, I had the strong impression that Anglophone philosophy did not pay much attention to the philosophy and theories of Karl Marx. He was regarded as a "dead dog". His work was rarely treated in the history of philosophy in the 1950s and 1960s or in survey courses in social and political philosophy, and the impression given was that history had moved beyond that nineteenth-century thinker — though notably not beyond Marx’s contemporary John Stuart Mill. Neglect and disrespect were the primary features of Marx's presence within philosophy in that period, it seemed. To many students gaining their philosophical and political identities in the 1960s, this seemed to be both arrogant and ignorant on the part of the discipline; philosophers in this tradition simply did not pay attention to the details of Marx's theories in spite of the grave social and economic issues of the day. Studying Marx carefully, as a philosopher might study Aristotle or Spinoza, was looked at as a waste of time.
Possibly the Cold War had something to do with this disdain within analytic philosophy; it is possible that the antagonism between the US and the USSR, representing liberal capitalism and communism, filtered into the profession of philosophy for a few decades. Certainly the crimes of Stalinism and Soviet Communism were considered a blot against Marx's ideas. Another relevant factor is the availability of texts from Marx's corpus: many important texts in which Marx expressed some of his key ideas were either unpublished or untranslated through the 1970s. (Marx's Grundrisse only appeared in English in 1973.)
This situation of neglect in the 1950s and early 1960s did not extend back into the 1930s. In those earlier decades some philosophers took an active and professional interest in Marx's ideas, including John Dewey, Morris R. Cohen, Bertrand Russell, and Sidney Hook discussed earlier (link). And what is most striking in that earlier philosophical debate about Marxism is the high quality of understanding that all these contributors had of Marx's social and economic theories. This level of familiarity was not to be found in philosophy again until the 1980s and 1990s.
Sidney Hook's account in the 1934 debate of Marx's analysis of the sociological circumstances of capitalism in The Meaning of Marx (link) is worth reading by itself. Hook did an excellent job of capturing Marx's views about the intricacies of an economic system divided between owners of productive forces and owners of labor-power (39-45). Hook showed a detailed understanding of the premises and assertions of Marx's theories of history, politics, and political economy, based on extensive textual knowledge. Hook plainly had exerted himself in studying the details of Marx's writings (those available in the 1920s and 1930s in German or English).
Marx was not featured at all in the course in social and political philosophy I took at the University of Illinois in 1968 or 1969. Some of Marx's ideas were included in the survey course on the history of social and political philosophy that John Rawls taught at Harvard for many years, including the years 1971-1976 when I was a graduate student in his department. In an earlier post I have reviewed the material and ideas that Rawls included in the several lectures on Marx's thought; and during the early 1970s these materials were quite limited (link). Their primary focus was on the Economic and Philosophic Manuscripts and Marx's theory of alienation. Rawls also discussed Marx's polemical essay "On the Jewish Question". There the main focus was on the distinction between political emancipation and full human emancipation. The lectures devoted to Marx that are collected in Lectures on the History of Political Philosophy were written sometime after 1984, according to Sam Freeman’s notes in the introduction to the volume, and they provide the student with more understanding of Marx’s theory of how a class society works, how capitalism is a system of exploitation and domination, and how the labor theory of value served Marx’s purpose of showing how that system worked. But even the final versions of the lectures do not indicate a broader range of either Marx’s texts or current secondary sources on Marx’s thought. Probably half of the content of these later lectures focused on one question that emerged in the analytic Marxism literature and was of special interest to Rawls: “Did Marx believe capitalism is unjust?”.
It might reasonably be argued that philosophers in the seventies had defined their discipline in ways that made them honestly doubtful that Marx’s writings made a substantial contribution to their discipline — however important they might be to sociology or history. Marx’s theories were not, after all, a continuation of the social contract tradition (Hobbes, Locke, Rousseau), and his empirical and historical claims about the modern world were not primarily normative. Normative ethical theory was just in the process of moving beyond “meta-ethics” (“Three Ways of Spilling Ink”), and perhaps Anglophone philosophy was not ready for a conceptual revolution within which social philosophy needed to be both normative and empirically substantive. Moreover, if we thought of Marx simply as a post-Hegelian philosopher of social dialectics, as H.B. Acton did (link), this neglect might well be deserved. So maybe the neglect of Marx was not entirely ideological, but more a question of “knowledge frameworks” or paradigm shifts. Marx’s theories did not fit readily into the conceptual frameworks of mainstream Anglophone philosophy. (Imagine J.L. Austin trying to make sense of the Grundrisse.) But that paradigm shift did eventually occur, and social philosophers came to recognize the ground they needed to share with social scientists, biologists, and historians — including Marx. Substantive theories about how the world works — including the social world — are indeed relevant to the main problems of social and political philosophy.