So there's a very big difference between X hasn't happened yet and X is factually impossible. Imagine standing there in 1750s and saying "we know for a fact that the human species is fundamentally incompatible with flight". Very shortly you would look like the complete arse that making that statement made you.
I don't dispute nobody has achieved the utopia Marx hypothesised, that is trivial to demonstrate, I'm asking how on earth you would establish fundamental incompatibility.
Actually the current prevailing theory is that primitive communism was the state humans lived in before the founding of the first proto states, so if anything your stance should be that evidence suggests humans are fundamentally compatible with communism, unless you mean to argue we have undergone some shift in our fundamental nature in which case I would again ask where your evidence is.