Once the idea has arisen that all ideas are merely the accompanying shadows of various social classes, groups, races, etc, cast in the light of their fixed interests, then another idea may very well present itself: that the only — or at least the surest, quickest, and most effective — way to get rid of an idea is to get rid of the class, group, race, etc, in whose interest it is said to be an ever-attendant shadow. 
.....The observation that persons of certain ranks, stations, groups, etc, will tend to express some ideas that sit well with their interests is, of course, old; but the inflexible, universal, and theoretical formulation of it is of relatively recent origin; whereunder, with the licence and urgency of revolution, men of that stamp have been quick to draw the conclusion that argument, persuasion, even “re-education” are slow, inefficient, and ultimately futile means by which to eradicate opposing ideas, so long as the social classes, groups, races, etc, that give rise to them remain. As the founder of the Cheka put it:
[C]ouldn’t this correlation [of ideas with social classes] be altered? Say, through the subjection or extermination of some classes of society? 
Radical-revolutionaries, for all their idealism, are still practical people, and, given that they see no moral obstacles around which they must go, since the overriding good is the end towards which they strive, they tend to adopt the most direct route to their destination. As Lichtenberg noted sardonically during the French Revolution:
With conversions, one usually seeks to get rid of the opinion, without offending the head; in France one now acts in a shorter way: one takes away the opinion together with the head. 
Naturally, the process of mass-killing needn't be anything personal, for, given the premise, and in the absence of stricture or moral scruple, it can simply be an instrumental process towards a desired end, strictly business, ideally conducted as efficiently as possible, though perhaps with a modicum of indulgence to any humane sensitivities that might remain.
Extermination must be put on a scientific basis if it is ever to be carried out humanely and apologetically as well as thoroughly. 
So wrote George Bernard Shaw, the renowned playwright and noted humanitarian. Perhaps he had got out of bed on the wrong side that morning, and boiled his breakfast-egg a minute too long. I know I’ve had mornings like that.
 Socialist intellectuals were the first advocates of mass-extermination as official social policy, conceived as the precondition of progress. As George Watson points out: “In the European century that began in the 1840s, from Engels’s article of 1849 down to the death of Hitler, everyone who advocated genocide called himself a socialist, and no exception has been found.” (George Watson, The Lost Literature of Socialism (Cambridge: The Lutterworth Press, 1998), p.80.) The reader can accept the challenge, and see if he can find an exception.
 Feliks Dzerzhinsky, quoted by George Leggett, The Cheka: Lenin’s Political Police (Oxford: Clarendon Press, 1981), p.252, quoted by Paul Bogdanor, “The Communists as They Really Are”, The Bloodbath Left. http://www.paulbogdanor.com
 G.C. Lichtenberg, Sudelbücher (Frankfurt am Main und Leipzig: Insel Verlag, 1984), I/242,1 from Sudelbuch K, (1793), p.469. [“Sonst sucht man bei Bekehrungen die Meinung wegzuschaffen, ohne den Kopf anzutasten; in Frankreich verfährt man jetzt kürzer: man nimmt die Meinung mitsamt dem Kopf weg.”]
 George Bernard Shaw, Preface to On the Rocks: A Political Comedy (1933), republished online by Project Gutenberg. Therein also: “The notion that persons should be safe from extermination as long as they do not commit wilful murder, or levy war against the Crown, or kidnap, or throw vitriol, is not only to limit social responsibility unnecessarily, and to privilege the large range of intolerable misconduct that lies outside them, but to divert attention from the essential justification for extermination, which is always incorrigible social incompatibility and nothing else.” [. . .] “[T]he planners of the Soviet State have no time to bother about moribund questions; for they are confronted with the new and overwhelming necessity for exterminating the peasants, who still exist in formidable numbers. . . . For a Communist Utopia we need a population of Utopians; and Utopians do not grow wild on the bushes nor are they to be picked up in the slums: they have to be cultivated very carefully and expensively. Peasants will not do . . .”. Cf., H.G. Wells, another Fabian socialist: “The men of the New Republic will not be squeamish, either, in facing or inflicting death . . . They will have an ideal that will make killing worth the while . . .”. H.G. Wells, Anticipations, Of the Reaction of Mechanical and Scientific Progress upon Human Life and Thought (London: Chapman & Hall, 1902), p.300, reproduced online by Project Gutenberg.