This is mostly correct, although the correct translation for him would be the ruling class.

It was far more broad, attacking ones citizen neighbors simply because they were landowners, for example.

Never. One's neighbors are one's allies in the class struggle against the ruling class. Landowners would never be the "neighbors" of a peasant in Czarist Russia. More precisely, it would be a war waged beneath the underclass (in Russia, the serfs and such) and the ruling class. I think you have your view of history tainted by modern preconceptions. Also, you have to be careful of certain translations. Das Kapital and Manifest der Kommunistischen Partei in the original German lead to certain nuances of language that can be lost in a poor translation. Moore's is probably the best, although not perfect.

The results of "communist" revolutions of the 20th century are orders of magnitude greater than the fallout of any other revolution, before or since.

Oh, so the October Revolution (Октябрьская революция) had many more casualties than the American Revolution? Or the French Revolution (Liberté, égalité, fraternité!)? Or the American Civil War? Well, no. The incidents to which you refer are the massacres conducted by despotic rulers in so-called Communist countries. In fact, they weren't even called "Communist". They were Stalinist. Or Maoist. You hang these acts around Marx's neck like a noose but he didn't advocate them and would never approve. Marx didn't advocate massacre or mass slaughter or starvation (of the proletariat, no less!). He advocated violent revolution. Once that was done, however, the state was under the control of the people and no more violence was necessary than that needed to keep the peace. And Pol Pot? Pol Pot wasn't even remotely Marxist. Most of the Khmer Rouge attacks were targeted at the intellectuals. The intellectuals?! These were Marx's people! The intellectuals were necessary to help build a global Communist free state. Marx certainly didn't advocate killing himself.

You see, you have mistaken the acts of depravity that are the responsibility of the ones who committed them as done under the order of the "eternal Marx." In truth, Marx was nothing more than a name and a scapegoat. The people who committed these actions were stark, raving mad and committed most of them out of personal prejudice and thirst for power and control. As far as history goes, nothing out of the ordinary.