As we have already noted, you claim that Beams’ “seriously misguided” views on utopianism are “indicative of prevailing (and longstanding) opinion within the Marxist movement...” Beams’ errors, moreover, arise from “the tension between science and utopianism that turned the latter into a virtual taboo.” You state that Beams is the latest in a long line of revisionists, dating back to the Second International in the late nineteenth century, who have falsely claimed that Marx and Engels were hostile to utopianism, in order to advance their own anti-revolutionary reformist agendas. Citing an extract from The Civil War in France (which Marx wrote in 1871 in defense of the Paris Commune), you assert:
The relationship between utopianism and Marxism as it is presented in this passage is markedly different from the way that relationship is usually presented by Marxists. By the latter I mean essentially the view that once Marxism had made socialism into a science, utopianism became irrelevant. The primary text on which this view is based is Engels’ Socialism: Utopian and Scientific, and there is no question that there, as elsewhere, both he and Marx subjected utopian socialism to a profound critique that was crucial to the whole project of a scientific socialism. But that critique didn’t render utopianism irrelevant, any more than the advent of Marxism rendered Hegel’s philosophy or Smith and Ricardo’s political economy irrelevant.
Your introduction of the word “irrelevant” is a terminological sleight of hand. The issue is not whether the ideas of the great utopian socialists are “irrelevant.” Nick Beams made no such statement. “Irrelevant” is not a word that students of intellectual history apply to works of great thinkers of the past. Every new generation of thinkers stands on the foundations laid down by those who preceded it. A deep understanding of Marxism requires the critical assimilation of the entire antecedent history of socialist thought, from Plato to the utopians of the late eighteenth and early nineteenth centuries. However, an appreciation of the contribution of past thinkers does not mean that their theories can be utilized, in their historically given form, in contemporary conditions.
Marx and Engels acknowledged, on numerous occasions, the immense intellectual debt that modern scientific socialism owed to the great utopians Saint-Simon, Fourier and Owen. They also explained at great length the historically-conditioned character and limitations of their predecessors’ contributions. As Engels wrote, the utopians “were utopians because they could be nothing else at a time when capitalist production was as yet so little developed. They necessarily had to construct the elements of a new society out of their own heads, because within the old society the elements of the new were not as yet generally apparent; for the basic plan of the new edifice they could only appeal to reason, just because they could not as yet appeal to contemporary history.” 
Your claim that the views of Marx and Engels on the subject of utopianism have been misrepresented by subsequent generations—that is, that their supposed hostility to utopianism has been exaggerated—is without foundation. Anyone who has access to their Collected Works can easily locate innumerable citations in which their critical attitude toward utopianism is precisely formulated. Paying necessary respect to its contribution to the development of socialism, they insisted that utopianism belonged to the past, not the present or the future, of the revolutionary socialist movement. This is the very point made in the passage from The Civil War in France that you quote. How you, Comrade Brenner, can claim that this passage supports your potted interpretation of Marxism is beyond me. It explains that the epoch of utopianism ended precisely at the point when the maturation of capitalism brought the working class into existence as a revolutionary force. The position is made even more explicit when one includes the four sentences that precede the extract you cite:
All the Socialist founders of Sects belong to a period in which the working class themselves were neither sufficiently trained and organized by the march of capitalist society itself to enter as historical agents upon the world’s stage, nor were the material conditions of their emancipation sufficiently matured in the old world itself. Their misery existed, but the conditions of their own movement did not yet exist. The utopian founders of sects, while in their criticism of present society clearly describing the goal of the social movement, the supersession of the wages system with all its economical conditions of class rule, found neither in society itself the material conditions of its transformation nor in the working class the organized power and the conscience of the movement. They tried to compensate for the historical conditions of the movement by phantastic pictures and plans of a new society in whose propaganda they saw the true means of salvation. 
It is at this point that you pick up the citation:
From the moment the workingmen class movement became real, the phantastic utopias evanesced, not because the working class had given up the end aimed at by these Utopists, but because they had found the real means to realize them, but in their place came a real insight into the historic conditions of the movement and a more and more gathering force of the military organization of the working class. But the last 2 ends of the movement proclaimed by the Utopians are the last ends proclaimed by the Paris Revolution and by the International. Only the means are different and the real conditions of the movement are no longer clouded in utopian fables. 
To all those who can understand what they read, it is perfectly clear that Marx is arguing that utopianism belongs to an earlier stage in the development of socialism, one that has been overtaken and superseded by the development of capitalism and the emergence of a mass working class.
For Marx, the Paris Commune of 1871 represented the supreme historical substantiation of the struggle he had waged over nearly thirty years, in opposition to myriad forms of utopianism, to place socialist theory on a scientific basis. The theoretical work of Marx and Engels between 1843 and 1847—whose greatest achievement was the critique of Hegelian idealism and, on this basis, the elaboration of the materialist conception of history—laid down the philosophical and political foundations of the modern socialist movement. This period of intense intellectual labor culminated in the writing of The Communist Manifesto. During the next twenty years, Marx devoted his energies almost entirely to the scientific substantiation of the revolutionary perspective that it advanced. This substantiation consisted principally of: (1) the successful utilization of the materialist conception of history as an instrument of political analysis (making possible the demystification and rational comprehension of political developments, such as the notorious coup d’etat of December 1851 that established the dictatorship of Louis Bonaparte), and (2) the discovery of the economic laws governing the motion of capitalist society, culminating in the publication of the first volume of Capital in 1867.
The most splendid narration of the origins of Marxism is to be found in Engels’ Socialism: Utopian and Scientific. I will cite only the most relevant passage:
Hegel had freed history from metaphysics—he had made it dialectic; but his conception of history was essentially idealistic. But now idealism was driven from its last refuge, the philosophy of history; now a materialistic treatment of history was propounded, and a method found of explaining man’s “knowing” by his “being,” instead of, as heretofore, his “being” by his “knowing.”
From that time forward Socialism was no longer an accidental discovery of this or that ingenious brain, but the necessary outcome of the struggle between two historically developed classes—the proletariat and the bourgeoisie. Its task was no longer to manufacture a system of society as perfect as possible, but to examine the historico-economic succession of events from which these classes and their antagonism had of necessity sprung, and to discover in the economic conditions thus created the means of ending the conflict. But the Socialism of earlier days was as incompatible with this materialistic conception as the conception of Nature of the French materialists was with dialectics and modern natural science. The Socialism of earlier days certainly criticised the existing capitalistic mode of production and its consequences. But it could not explain them, and, therefore, could not get the mastery of them. It could only simply reject them as bad. The more strongly this earlier Socialism denounced the exploitation of the working-class, inevitable under Capitalism, the less able was it clearly to show in what this exploitation consisted and how it arose. But for this it was necessary—(1) to present the capitalistic method of production in its historical connection and its inevitableness during a particular historical period, and therefore, also, to present its inevitable downfall; and (2) to lay bare its essential character, which was still a secret. This was done by the discovery of surplus-value. It was shown that the appropriation of unpaid labour is the basis of the capitalist mode of production and of the exploitation of the worker that occurs under it; that even if the capitalist buys the labour-power of his labourer at its full value as a commodity on the market, he yet extracts more value from it than he paid for; and that in the ultimate analysis this surplus-value forms those sums of value from which are heaped up the constantly increasing masses of capital in the hands of the possessing classes. The genesis of capitalist production and the production of capital were both explained.
These two great discoveries, the materialistic conception of history and the revelation of the secret of capitalistic production through surplus-value, we owe to Marx. With these discoveries Socialism became a science. The next thing was to work out all its details and relations. 
During the early years of the German Social Democratic Party, Marx and Engels were brutally critical of any tendency expressing a retreat from these theoretical conquests. In the climate of political reaction that followed the suppression of the Paris Commune of 1871 and the consolidation of Bismarck’s German empire, they had to repeatedly contend with political-ideological currents that sought to revive antiquated doctrines refuted decades earlier by Marx and Engels. On October 19, 1877, Marx penned an angry complaint to his friend Friedrich Adolph Sorge, who was living in Hoboken, New Jersey:
In Germany a corrupt spirit is asserting itself in our party, not so much among the masses as among the leaders (upper class and “workers”). The compromise with the Lassalleans has led to further compromise with other waverers; in Berlin (via Most) with Dühring and his “admirers,” not to mention a whole swarm of immature undergraduates and over-wise graduates who want to give socialism a “higher, idealistic” orientation, i.e., substitute for the materialist basis (which calls for serious, objective study if one is to operate thereon) a modern mythology with its goddesses of Justice, Liberty, Equality and Fraternité. Dr. Höchberg  the gentlemen who edits the Zukunft [Future], is a representative of this tendency and has “bought his way” into the party—no doubt with the “noblest” of intentions, but I don’t give a fig for “intentions.” Seldom has anything more pitiful than his programme for the Zukunft been ushered into the world with more “modest pretensions.”
The workers themselves, when like Mr Most and Co. they give up working and become literati by profession, invariably wreak “theoretical” havoc and are always ready to consort with addle-heads of the supposedly “learned” caste. In particular, what we had been at such pains to eject from the German workers’ heads decades ago, thereby ensuring their theoretical (and hence also practical) ascendancy over the French and English,—namely Utopian socialism, the play of the imagination on the future structure of society,—is once again rampant and in a far more ineffectual form, not only as compared with the great French and English Utopians, but with—Weitling.  It stands to reason that Utopianism which bore within itself the seeds of critical and materialist socialism, before the advent of the latter, can now, post festum, only seem silly, stale and thoroughly reactionary. 
This passage is a concise summation of Marx’s estimate of efforts to reintroduce utopianism into the socialist movement. Yes, it is true that Beams’ disavowal of utopianism represents, as you, Comrade Brenner, state, “prevailing (and longstanding) opinion within the Marxist movement.” But if this “opinion” is “misguided,” your differences are, first and foremost, with Marx and Engels rather than with Nick Beams.
Marx-Engels Collected Works, Volume 25 (New York: International Publishers, 1987), p. 253.
Marx-Engels Collected Works, Volume 22 (New York: International Publishers, 1986), p. 499.
ibid., pp. 499–500.
Marx-Engels Collected Works, Volume 24 (London: Lawrence & Wishart, 1989), pp. 304–305.
Karl Höchberg (1853–1885) was a wealthy supporter of the socialist movement.
Wilhelm Weitling (1808–1871) was one of the earliest leaders of the young workers movement in Germany in the late 1830s and 1840s. He promoted a form of utopian communism that Engels described as “sentimental Love-mongering.”
Marx-Engels Collected Works, Volume 45 (Moscow: Progress Publishers, 1991), pp. 283–284.