Had Sancho [Stirner] understood the fact that within the framework of definite modes of production , which, of course, are not dependent on the will, alien practical forces, which are independent not only of isolated individuals but even of all of them together, always come to stand above people — then he could be fairly indifferent as to whether this fact is preserved in the religious form or distorted in the fancy of the egoist, above whom everything is placed in imagination, in such a way that he places nothing above himself. Sancho would then have descended from the realm of speculation into the realm of reality, from what people fancy to what they actually are, from what they imagine to how they act and are bound to act in definite circumstances. What seems to him a product of thought , he would have understood to be a product of life . He would not then have arrived at the absurdity worthy of him — of explaining the division between personal and general interests by saying that people imagine this division also in a religious way and seem to themselves to be such and such, which is, however, only another word for "imagining". -- KM, The German Ideology

These arguments take material relations and equate them to ideas. As usual it doesn't matter what nonsense you believe, as long as you don't believe in communism. As such, the argument that one could equate a material relation with an idea is itself an idealistic, practically religious conceptualization. Basically, Pretending material relations are just ideas. The critiques he makes would be more appropriately turned on his own "religious" idealism.

There's no criticism that Marx didn't anticipate, if these sophists bothered to read they would know that instead of trotting out the same tired old lies for the last 150+ years. Its sad.