I suppose on this bbs I'm the closest thing to an authority on the part of the scientifically inclined Left, but that's not the real deal. If really interested in the topic, you should read up yourself.
Yes, it's true that many want to identify capitalism, the current way of life, with God's plan or natural law. Thus, only those mysterious, uncaused departures from human nature like feudalism or slavery need to be named. Political embarrassments like the British Empire or Fanco's Spain also get named something else. There seems to be a vague notion that although capitalism is the expression of the human spirit writ large, people in the past were too deficient to do things the right way. And any embarrassments from modern times, like WWI, are just inexplicable. Naming capitalism tends to imply that there can be something else, hence is frowned upon.
But, no, "Communism" has no problem at all with the concept of human nature, holding very strongly that we all have it.
It is a matter of historical fact that it's other political movements which hold that various humans have different natures. I believe the evil consequences of this kind of thinking are horribly obvious, but the factual evidence for it, nil. I think the so-called blank slate fallacy is a sweet-sounding name for a concept of human inequality.
The kind of people who promote this notion are quite cautious about telling us what they think is written on the slate. But as I read them, in practice the commandments written on the slate only come in two varieties. One set is pretty much identical with whatever the proponents imagine necessary to justify the current social order. And the other set imagines whatever is needed to justify a return to the past.
Both varieties tend to identify what is unnatural with what ordinary people would just call progressive or socialist. Curiously, although the natural order would appear to need no more enforcement than the law of universal gravitation, neither set ever wonders how the non-blank slate could be overwritten. None
of these people have ever
provided any sound scientific evidence demonstrating the existence of whatever they imagine to be written on the slate. Not even the incest taboo, which is about as close to a cultural universal you can get!