“The firmest proof that Marxism is not science but an ideology is Marxism’s attitude to the experience of the real communist (or socialist) societies.”

Source: The Birth of Fascist Ideology: From Cultural Rebellion to Political Revolution, 1994, p. 5

New Preface, p. v
Main Currents Of Marxism (1978)

Source: Russia Under The Bolshevik Regime (1994), p. 245

On the Social State of Marxism (1978)

Source: "How to Be a Good Communist - 4. The Unity of Theoretical Study and Ideological Self-Cultivation" https://www.marxists.org/reference/archive/liu-shaoqi/1939/how-to-be/ch04.htm (July 1939)

On the Social State of Marxism (1978)

Anarchism or Socialism (1906)
Context: We are not the kind of people who, when the word "anarchism" is mentioned, turn away contemptuously and say with a supercilious wave of the hand: "Why waste time on that, it's not worth talking about!" We think that such cheap "criticism" is undignified and useless.
Nor are we the kind of people who console themselves with the thought that the Anarchists "have no masses behind them and, therefore, are not so dangerous." It is not who has a larger or smaller "mass" following today, but the essence of the doctrine that matters. If the "doctrine" of the Anarchists expresses the truth, then it goes without saying that it will certainly hew a path for itself and will rally the masses around itself. If, however, it is unsound and built up on a false foundation, it will not last long and will remain suspended in mid-air. But the unsoundness of anarchism must be proved.
Some people believe that Marxism and anarchism are based on the same principles and that the disagreements between them concern only tactics, so that, in the opinion of these people, no distinction whatsoever can be drawn between these two trends.
This is a great mistake.
We believe that the Anarchists are real enemies of Marxism. Accordingly, we also hold that a real struggle must be waged against real enemies.

Interview with George Sylvester Viereck, 1923 https://www.theguardian.com/theguardian/2007/sep/17/greatinterviews1 <br class="br">1920s <br class="br">Context: Socialism is the science of dealing with the common weal. Communism is not Socialism. Marxism is not Socialism. The Marxians have stolen the term and confused its meaning. I shall take Socialism away from the Socialists. Socialism is an ancient Aryan, Germanic institution. Our German ancestors held certain lands in common. They cultivated the idea of the common weal. Marxism has no right to disguise itself as socialism. Socialism, unlike Marxism, does not repudiate private property. Unlike Marxism, it involves no negation of personality, and unlike Marxism, it is patriotic. We might have called ourselves the Liberal Party. We chose to call ourselves the National Socialists. We are not internationalists. Our socialism is national. We demand the fulfilment of the just claims of the productive classes by the state on the basis of race solidarity. To us state and race are one.

Speech (20 December 1961) http://www.cuba.cu/gobierno/discursos/1961/esp/f201261e.html