In both your document, Comrade Brenner, and your joint letter, you repeatedly claim that the opposition to utopianism in the era of the Second International was largely a product of the growth of opportunism. You write:
Science in the prewar Second International was not just a disinterested development of theory (as North seems to believe); it was increasingly an alibi for absconding from revolutionary responsibilities, which “objective conditions” would supposedly take care of. Hence the need to turn utopianism into a virtual taboo, because it threatened, not science but rather this objectivism. In the actual development of Marxism, however, scientific socialism was a dialectical “aufheben” [cancelling out] of its utopian predecessors, and utopia and science were not a rigid dichotomy but a unity of opposites, which is readily apparent in such canonical works as Critique of the Gotha Program or State and Revolution, to say nothing of a little gem like Paul Lafargue’s The Right to be Lazy.
This account of the origins of anti-utopianism, buttressed by pseudo-dialectical, bilingual phrasemongering is essentially false.
The manner in which you employ Hegelian phraseology is sophistry of the purest water. In place of a real explanation of the relationship between utopianism and Marxism, you resort to terms such as aufheben and “unity of opposites.” This is simply a means of saying nothing, and making it appear profound. An example of the misuse to which pseudo-dialectical phraseology lends itself is shown in your invocation of Marx’s Critique of the Gotha Program and Lenin’s State and Revolution. These works, you say, demonstrate that utopianism and Marxism are a “unity of opposites.” What precisely does this mean? There is nothing utopian about either of these works (or even, except for certain stylistic devices that draw upon the literary tradition of Fourier and Proudhon, about Lafargue’s The Right to be Lazy, which is, at any rate, a rather minor work). Marx’s Critique was written for the express purpose of demarcating his own scientific conceptions from all traces of the type of petty-bourgeois eclecticism and utopianism that characterized the conceptions of the Lassalleans. For example, Marx subjected the Lassallean’s pledge of a “fair distribution” of the “proceeds of labor” to a withering criticism, insisting, in opposition to all utopian illusions, that “Right can never be higher than the economic structure of society and its cultural development which this determines.” In justifying his severe attitude to various imprecise and/or incorrect formulations, Marx wrote that this stance was necessary:
… to show what a crime it is to attempt, on the one hand, to force on our Party again, as dogmas, ideas which in a certain period had some meaning but have now become obsolete verbal rubbish, while again perverting, on the other, the realistic outlook, which it cost so much effort to instil into the Party but which has now taken root in it, by means of ideological, legal and other trash so common among the Democrats and French Socialists. 
Lenin’s State and Revolution elaborates a theory of the state on the basis of a comprehensive review of the writings of Marx and Engels on the subject. As in all the great “canonical works” (your phrase, Comrades Steiner and Brenner, not mine), Lenin explicitly and directly counterposes the scientific attitude of Marx to that of utopianism. As Lenin explains in one important and oft-quoted passage:
There is no trace of utopianism in Marx, in the sense that he made up or invented a “new” society. No, he studied the birth of a new society out of the old, and the forms of transition from the latter to the former...
We are not utopians. We do not “dream” of dispensing at once with all administration, with all subordination. These anarchist dreams, based upon incomprehension of the tasks of the proletarian dictatorship, are totally alien to Marxism, and, as a matter of fact, serve only to postpone the socialist revolution until people are different. No, we want the socialist revolution with people as they are now [emphasis added], with people who cannot dispense with subordination, control and “foremen and accountants”. 
This latter passage is particularly apposite as a response to your claim that a socialist revolution requires the psychological reconditioning of the population.
Bernstein was not an enemy of utopianism. He argued against the conception that the socialist movement needed to legitimize its existence on the basis of science. He wrote:
There is no doubt that, although socialism as a practical proletarian movement has piled success upon success in many countries, formulating its position in ever clearer fashion, it experienced major setbacks as a scientific theory, losing its conceptual coherence and security in the cacophonous doubts and confusions of its representatives. Thus the legitimate question arises as to whether there exists an internal connection between socialism and science. To this concern regarding the possibility of a scientific socialism, I would like to add the question of whether a scientific socialism is needed at all. 
Bernstein did not believe it was necessary, or even desirable, that Marxism deny its links to utopianism, which he argued were necessarily present in a socialist movement. “However, whether one defines it as a condition, a theory, or a movement,” he wrote, “socialism is always pervaded by an idealistic element that represents either the ideal itself or the movement toward such an ideal. Thus socialism is a piece of the beyond—obviously not beyond the planet we live on but beyond that of which we have positive experience.” 
Your claim that “It is Bernstein who pushes the counterposing of utopianism to science to its logical conclusion” is simply a misrepresentation of what the founder of modern revisionism wrote. He explained with great care that he did not employ the term utopian “as a euphemism for unrealistic dreams and fantasies.” Such a use of the term, he protested, “would be a great injustice to those three great nineteenth-century utopians and forerunners of modern socialism…”  Far from presenting utopianism and Marxism as opposites, Bernstein argued: “If we investigate and compare the theories of these three utopians [Owen, Saint-Simon and Fourier] with Marx’s theory, we shall find that Marx developed and emphasized the scientific element to a higher degree. But neither in the utopian writings nor in Marx’s teachings is science everything. Of course, Marx draws narrower boundaries around the realm of will, imagination, and inclination, but he does not fully erase it.” 
Bernstein accused Engels of having exaggerated the chasm between the work of Marx and his utopian predecessors. “On one hand he casts the utopians in an unfavorable light by overemphasizing the role of imagination in their writings, although they actually stressed discovery over invention. On the other he proclaims modern socialism free of any form of invention. In my opinion socialism has never been, nor can it ever be, ‘free of inventions and imaginings.’” 
As these passages make clear, Bernstein recognized that the main challenge to his revisionist project stemmed, not from utopianism but from the identification of socialism with science. In attacking the “objectivism” and “abstentionism” of the ICFI, it is you who are echoing the positions of Bernstein. Moreover, your repeated call for the revival of “socialist idealism” as the programmatic basis of a new socialist culture, places you entirely within the camp of the revisionists on a key philosophical issue. Underlying the entire “Back to Kant” movement, which began in the late 1860s and ultimately played a major role in shaping the theoretical outlook of Bernstein and his supporters, was the conception that the struggle for socialism did not require scientific substantiation. The invocation of moral ideals—such as that which finds expression in Kant’s second formulation of the categorical imperative (“Act in such a way that you always treat humanity, whether in your own person or in the person of any other, never simply as a means, but always at the same time as an end.”)—could serve the struggle for socialism just as well as the Marxian conception of historical determinism. Indeed, a section of left academics in late nineteenth century Germany, such as Karl Vorländer, argued that the socialist movement ought to trace its philosophical lineage to Kant. In your own ill-informed haste to overthrow basic historical conceptions of Marxism, you have little concern for the theoretical roots and implications of your own arguments.
Marx-Engels Collected Works, Volume 24, p. 87.
V.I. Lenin, Collected Works, Volume 25, p. 430.
“How is Scientific Socialism Possible,” in Selected Writings of Eduard Bernstein, 1900–1921, ed. and trans. Manfred Steger (New Jersey: Humanity Books, 1996), p. 94.
ibid., p. 95.
ibid., p. 96.
ibid., p. 97.