What has passed for "materialism" in traditional Marxism—the division between material "infrastructure" and ideal "superstructure," is itself a perverse form of idealism. Granted, those who practice law, or music, or religion, or finance, or social theory, always do tend to claim that they are dealing with something higher and more abstract than those who plant onions, blow glass, or operate sewing machines. But it's not really true. The actions involved in the production of law, poetry, etc., are just as material as any other. Once you acknowledge the simple dialectical point that what we take to be self-identical objects are really processes of action, then it becomes pretty obvious that such actions are (a) always motivated by meanings (ideas); and (b) always proceed through a concrete medium (material). Further, that while all systems of domination seem to propose that "no, this is not true, really there is some pure domain of law, or truth, or grace, or theory, or finance capital, that floats above it all," such claims are, to use an appropriately earthy metaphor, bullshit. As John Holloway (2003) has recently reminded us, it is in the nature of systems of domination to take what are really complex interwoven process of action and chop them up and redefine them as discrete, self-identical objects—a song, a school, a meal, etc. There's a simple reason for it. It's only by chopping and freezing them in this way that one can reduce them to property and be able to say one owns them.
A genuine materialism then would not simply privilege a "material" sphere over an ideal one. It would begin by acknowledging that no such ideal sphere actually exists. This, in turn, would make it possible to stop focusing so obsessively on the production of material objects—discrete, self-identical things that one can own—and start the more difficult work of trying to understand the (equally material) processes by which people create and shape one another.
Noted: David Graeber
Also from "Turning Modes of Production Inside-Out":