The rise of capitalism was accompanied by a bitter struggle against the religious obscurantism of feudal reaction. The rationalists, the empiricists and the French materialists struck blow after blow against the dominant ideology of the day. The struggle for rational and scientific thought was an indispensable weapon in the bourgeois revolution.
Today however, the capitalist class has turned into a counter-revolutionary and conservative force. It has taken up the banner of idealism and turned against the revolutionary materialism which it relied on in the struggle against feudalism. Today, the struggle to defend science, materialism and rational thought is an essential part of the struggle for socialism. While the old bourgeois schools of thought have degenerated into irrationalism and mysticism, Marxism has managed to rescue their revolutionary kernel and raise them to a higher level in the philosophy of scientific socialism: dialectical materialism.
Recommended Reading: History of Philosophy, “The Renaissance”, “Descartes, Spinoza and Leibniz”