Marx and Engels fought utopian and idealistic versions of socialism

Marx and Engels fought to establish their theories from the laws of dialectical and historical materialism. They analysed the history of class society from its inception through to the revolutionary upheavals of mid-nineteenth century Europe and wrote the Communist Manifesto in opposition to various types of utopian and idealist “socialism”. They also wrote at length to refute the influential, but unscientific, views of Duhring and Proudhon.

The ideological struggles led by Marx and Engels resulted, as Lenin noted, in the defeat of “pre-Marxist socialism”.  From that point on, bourgeois efforts to turn the workers from revolution and proletarian dictatorship could no longer stand “on its own independent ground, but on the general ground of Marxism, as revisionism” (Lenin On Marxism and Revisionism).