I'm in the process of rereading Eco's The Name of the Rose, and I'm reminded that communism has its roots in a type of heretical Christianity. It's not that any one of these particular heresies constitutes the origins, but that communism is contained within this heretical trace, constantly under erasure, invisible, but continually mutating and putting the dominant structures of the society into crisis. At the same time, the violence of heresy continually can be redirected, shifting from the powerful to other members of the powerless. Eco gestures towards this through the anti-Semitic violence of the heretic Salvatore. Here are a couple moments in which Eco works through this history.
"I say that many of these heresies, independently of the doctrines they assert, encounter success among the simple because they suggest to such a people the possibility of a different life. I say that very often the simple do not know much about doctrine. I say that often hordes of simple people have confused Catharist preaching with that of the Patarines, and these together with that of the Spirituals. the life of the simple, Ado, is not illuminated by learning and by the lively sense of distinctions that makes us wise. And it is haunted by illness and poverty, tongue-tied by ignorance. Joining a heretical group, for many of them, is often only another way of shouting their own despair. You may burn a cardinal's house because you want to perfect the life of the clergy, but also because you believe that the hell he preaches does not exist. It is always done because on earth there does exist a hell, where lives the flock whose shepherds we no longer are. But you know very well that, just as they do not distinguish between the Bulgarian church and the followers of the priest Liprando, so often the imperial authorities and their supporters did not distinguish between Spirituals and heretics. Not infrequently, imperial forces, to combat their adversaries, encouraged Catharist tendencies among the populace. In my opinion they acted wrongly. But what I now know is that the the same forces often, to rid themselves of these restless and dangerous and too 'simple' adversaries, attributed to one group the heresies of the others, and flung them all on the pyre. I have seen--I swear to you, Abo, I have seen with my own eyes--men of virtuous life, sincere followers of poverty and chastity, but enemies of the bishops, whom the bishops thrust in the hands of the secular arm, whether it was in the service of the empire or of the free cities, accusing the men of sexual promiscuity, sodomy, unspeakable practices--of which others, perhaps, but not they, had been guilty. The simple are meat for slaughter, to be used when they are useful in causing trouble for the opposing power, and to be sacrificed when they are no longer of use."
Umberto Eco, The Name of the Rose, 152
"Scratch the heresy and you will find the leper. Every battle against heresy wants only this: to keep the leper as he is." Umberto Eco, The Name of the Rose, 203