Just because the Communist Manifesto calls for violence does not mean that everyone who self-identifies as communist has to accept it. Modern communists can change, re-interpret, or cherry-pick parts of the doctrine. I know at least one person who explicitly identifies as both a communist (small c) and a pacifist. Marx defined the original meaning of the word, but he doesn't control its definition through the end of history, and the modern conception of communism is the resulting economic system, not the means to achieve it. Hell, in some contexts, communism is a tool of literary analysis.

Communism (big C), in practice, has lead to a lot of slaughter. I can't deny that. However, to say that it has created "more misery and destruction than any other movement in history," I will provide the counter-point that it is the only significant social-historical movement to occur in the industrial age. The Crusades (to pick a Goodwin-level example) or even the French revolutions did not have the means to cause misery and destruction on such a scale. Controlling for that accident of historical (technological) context, I would need additional evidence or argument to convince me that Communism is significantly more malicious from any other abstract idea (including democracy in both ancient and recent time as well as most religions) that people have used as an excuse for killing each other over the years.