I was actually thinking more along the lines of Marx writing that the proletariat would rise up itself, perhaps even without violence, while disregarding the peasantry, while most Communist states were largely peasant states that became Communist due the actions of a small elite, or became Communist (at least partly) for other reasons, such as nationalism and colonialism, like in the case of Vietnam*. I'm not sure if a true Marxist revolution in the sense of the ever happened.
Then again, Marx himself denounced what he called Marxism, saying that he believed in many things but not Marxism... so what is even Marxism?
As for blame, that's a different matter. For instance, Stalins excesses were more rooted in his cult of personality, his paranoia and his prejudices than in his political beliefs, I'd say. Besides that, many of his policies went against Leninist ideals. And is the idea of democracy to blame for the Holocaust because the Nazi's were originally democratically elected? Or, if we accept Jesus as historical figure, is he to blame for all the horrors carried out by Christians? Or, taking that further, are the founders of Jewish monotheism to blame for everything bad done in the name of their religion, Christianity and Islam, being the root of all three? I'm just saying, this blame game is tricky business.
* = since this a book club, can I recommend Ho Chi Minh: A Life by William J. Duiker? I mean, if one's interested in that subject, it's a good book.