Throughout the civilized world the teachings of Marx evoke the utmost hostility and hatred of all bourgeois science (both official and liberal), which regards Marxism as a kind of “pernicious sect”. And no other attitude is to be expected, for there can be no “impartial” social science in a society based on class struggle. In one way or another, all official and liberal science defends wage-slavery, whereas Marxism has declared relentless war on that slavery. To expect science to be impartial in a wage-slave society is as foolishly naïve as to expect impartiality from manufacturers on the question of whether workers’ wages ought not to be increased by decreasing the profits of capital.

But this is not all. The history of philosophy and the history of social science show with perfect clarity that there is nothing resembling “sectarianism” in Marxism, in the sense of its being a hidebound, petrified doctrine, a doctrine which arose away from the high road of the development of world civilisation. On the contrary, the genius of Marx consists precisely in his having furnished answers to questions already raised by the foremost minds of mankind. His doctrine emerged as the direct and immediate continuation of the teachings of the greatest representatives of philosophy, political economy and socialism.

The Marxist doctrine is omnipotent because it is true.

https://www.marxists.org/archive/lenin/works/1913/mar/x01.htm

Trotsky declares: “It is an illusion” to imagine that Menshevism and Bolshevism “have struck deep roots in the depths of the proletariat”. This is a specimen of the resonant but empty phrases of which our Trotsky is a master. The roots of the divergence between the Mensheviks and the Bolsheviks lie, not in the “depths of the proletariat”, but in the economic content of the Russian revolution. By ignoring this content, Martov and Trotsky have deprived themselves of the possibility of understanding the historical meaning of the inner Party struggle in Russia. The crux of the matter is not whether the theoretical formulations of the differences have penetrated “deeply” into this or that stratum of the proletariat, but the fact that the economic conditions of the Revolution of 1905 brought the proletariat into hostile relations with the liberal bourgeoisie—not only over the question of improving the conditions of daily life of the workers, but also over the agrarian question, over all the political questions of the revolution, etc. To speak of the struggle of trends in the Russian revolutions distributing labels such as “sectarianism”, “lack of culture”, etc., and not to say a word about the fundamental economic interests of the proletariat, of the liberal bourgeoisie and of the democratic peasantry, means stooping to the level of cheap journalists. [Emphasis Added]

https://www.marxists.org/archive/lenin/works/1910/hmipsir/i.htm