Kant

One of the components of Marxism that led to much of its later confusion can be seen in Marx’s rejection of ethical idealism, a strain of Marx’s thinking that is too often disguised and unaddressed, and which invariably takes its idealistic fans by surprise, if it enters consciousness at all.
The grounds for all of this, beginning with Hegel, are complex, but finally stem from an inability to really grapple with the transcendental idealism of Kant.
From Sidney Hook’s From Hegel To Marx, Columbia, 1994, p.47
Rejection of Abstract Ethical Idealism

Opposition to the excesses of rabid individualism, however, comes not only from social realists but even more often from ethical idealists. Indeed it is in this latter form that it is most vocal and emphatic. What age has not heard a cry for justice in the name of Christ, Kant or some other ethical prophet? When has not someone’s conscience, someone’s devotion to things invisible led to conflict with the social order? And yet both Hegel and Marx regarded abstract ethical idealism, whether it have its roots in Christ, Rousseau or Kant, as Utopian and unreasonable-as even more dangerous than any philosophy of social atomism. It involved the same denial of the priority of the group over the individual; the same acceptance of the natural rights, or conscience, ethics which lies at the basis of philo¬sophical anarchism. Because it endangered the stability of the state, Hegel stamped it as a revolutionary doctrine; because it hampered militant class activity, Marx condemned it as Incipiently counter-revolutionary.

Amazon review of Kant’s Politics, on the issue of ‘Freedom’s Causality

Beginning of Harry Van Der Linden’s Kantian Ethics And Socialism, Hackett, 1988

Around the turn of the century the neo-Kantian socialist Hermann Cohen wrote in his Introduction and Critical Epilogue to Friedrich Albert Lange’s History of Materialism that Kant “is the true and real originator of German socialism.’” His claim, of course, is not to be taken too literally. After all, Kant to a large extent defended the minimal state and accepted the emerging capitalist market econ­omy, whereas socialists have typically rejected both. Rather, the point of Cohen’s challenging statement is that Kant’s practical phi­losophy contains moral and philosophical-historical insights cru­cial to socialist thought and that his notion of the highest good, or moral society of colegislators who seek to enhance one another’s ends, can be extrapolated to set forth the demand for the socialist ideal. Thus the statement suggests a conception of socialism that is ethical in nature and involves not a mere denial of liberal thought but rather its critical extension in the form of economic democracy. A final aspect of Cohen’s claim which needs to be stressed is its implicit criticism of Marx on the grounds that a morally defensible socialism is an ethical socialism and that the philosophical founda­tions of a tenable socialism are to be sought in Kant, not in Hegel.

Relevant to our consideration:
From The New Hegelians, Politics and Philosophy in the Hegelian School, ed. Douglas Moggach, Cambridge, 2006

In Religion within the Boundaries of Mere Reason Kant strips down the Christian religion to what he regards as its moral core. This is the pursuit of virtue with the aim of founding with all others a worldwide ethical commonwealth. Kant makes sit clear that he respects the work of churches and church leaders in trying to bring about this moral ideal, but he is equally clear that they do not represent the sole or, indeed, even the most important means in bringing it about. The general external trappings of religious faith Kant regards as, at best, symbolically representing the change at which true virtuous behaviour aims, and, at worst, seriously misleding the faithful in their goal of achieving goodness. Although Kant does not try to undermine entirely the metaphysical or transcendent side of religion, he does regard its role as secondary and dependent upon the pursuit of moral goals. It might be said with Kant that the essence of true religion, of which the best forms of Christian worship are part, is morality. Humanity is at the core of Kant’s interpretation of religion. It has to do with the perfection of the human race as the highest aspect of nature. With Kant, religion is moral anthropology. This brings him very close to Ludwig Feuerbach.

The question of the philosophy of history hovers ambiguously between Kant and Hegel. The study of the eonic effect adopts a variant of the Kantian concept as it appears in his essay on history, Idea For A Universal History, and proceeds to construct an eonic model, one that can bring a fresh perspective on the question of historical dynamics, so precariously analyzed by the ‘historical materialists’.

The subject of Hegelianism, as cited in the book by Toews, constitutes a kind of quagmire for leftist analysis, although the profundity of Hegel’s system cautions one against simplistic anti-Hegelian affirmations.

In fact, the eonic model adopts a kind of empirical, and evolutionary, approach to the core issue of the philosophy of history, proceeding from an entirely different direction, the result, however, generating a most remarkable echo of Hegel, with its construct of the ‘evolution of freedom’.

Hegelian study is, should we say it, quite arcane, with the result that few understand it, yet the eonic model performs at a glance what is needed, the demonstration of the evolutionary meaning of freedom. So we proceed to outflank Hegel, looking back to see that our approach will suddenly generate an understanding of what Hegel meant.  We are about our own business, which will, due to the circumstance of our subject, make Hegel a empirical fact of the very self-referential history we are subjecting to analysis. So we lose nothing, and, armed with the eonic model, can backtrack to reconstruct the remarkable moment, or period, from the 1790’s to the collapse of the Hegelian project in the 1840’s.

Our perspective includes far more than this, and we can as well play on the harp of liberal emergentism, complete with the strains of Yankee Doodle as we see the historical moment of the American Revolution.