The contribution of Karl Marx and Friedrich Engels to socialism was a theory that purported to show why the kingdom of equality was not only desirable and feasible but inevitable. To advance this claim, they resorted to methods borrowed from the natural sciences, which had gained immense prestige in the nineteenth century. Marx and Engels formulated a doctrine of “scientific socialism,” which asserted that the ideal of a propertyless, egalitarian society was something that not only should happen but, by virtue of the natural evolution of the economy, had to happen. The Marxist concept of social evolution arose under the influence of the Darwinian theory formulated in 1859 in On the Origin of Species. Darwin’s book depicted the emergence of biological species as due to a process of natural selection that enabled them better to survive in a hostile environment. The process was a dynamic one, evolving species from lower to higher stages according to determinable rules. This theory was quickly adapted by students of human behavior, giving rise to a school of “evolutionary sociology” that depicted history as a progression, “by stages,” from lower to higher forms. So great was Darwin’s influence on Marx that Engels, speaking at his friend’s funeral, said, “Just as Darwin had discovered the law of development of organic nature so did Marx discover the law of human history.”
The injection of evolutionary thinking into socialist theory introduced into it the element of inevitability. According to “scientific socialism,” human actions may somewhat retard or accelerate social evolution, but they cannot alter its direction, which depends on objective factors. Thus, for reasons that will be spelled out below, capitalism in time must inexorably yield to socialism. The emotional appeal of this belief is not much different from the religious faith in the will of God, inspiring those who hold it with an unshakable conviction that no matter how many setbacks their cause may suffer, ultimate victory is assured. It would hold especial attraction for intellectuals by promising to replace spontaneous and messy life with a rational order of which they would be the interpreters and mentors. As Marx put it in a celebrated dictum, “The philosophers have only interpreted the world in various ways: the point, however, is to change it.” And who is better qualified to “change” it intelligently than intellectuals? For all its formal commitment to the scientific method, Marxism violated its most basic feature, namely open-mindedness and a willingness to adjust theory to new evidence. (Bertrand Russell called Bolshevism, an offspring of Marxism, a “religion” and spoke of its “habit of militant certainty about objectively doubtful matters.”) It was a rigid doctrine, dismissive of different views. Marx made no secret of his attitude toward those who disagreed with him: criticism, he once wrote, “is not a scalpel but a weapon. Its object is the enemy, [whom] it wishes not to refute but to destroy.” Marxism thus was dogma masquerading as science.
The similarity between Marxism and neoconservatism might be expressed in the following way: both perspectives say that certain injustices can't be cured under our present system of political democracy and mixed economy. The Marxist concludes that we have to overthrow the present system and the neoconservative concludes that we have to live with the injustices. But they are both wrong.
Hilary Putnam, "How Not to Solve Ethical Problems" (1983)