Strangers in a strange land
Anyone associated with Marxism, at least in the United States, will have the sensation of living a science fiction novel, like being a stranger in a strange land. The idea is that what Marx was doing—and what Marxists after him need to do—is less the application of a particularly Marxian method (whatever it is called or however it is defined) and more the ongoing, ruthless critique of both mainstream economic thought and capitalism. Marx's point is that there's a fundamental injustice at the heart of capitalism, with all kinds of conditions and consequences for the rest of society. That's the essence (to use a much-maligned term) of Marx's critique of both mainstream economics and capitalism. He starts with their (and, today, our) fundamental propositions and ends in a very different place.