Of course, Marx and Engels were advocating genocide as early as the 1840s, expressing the hope that the Slavs of the Austro-Hungarian empire would be exterminated "down to their very names" because they weren't progressive enough. Fortunately, no one took them up on this. Stalin singled out several nations for wholesale deportation into the depths of the USSR, such as the Chechens, Ingush, Kalmyks and Crimean Tatars. His intention was not so much to annihilate them as to maim them permanently, trying to kill off as many as he could via the inhuman conditions of their transportation, then dumping them in Central Asia where they could safely be forgotten.
Pol Pot would dearly have loved to exterminate the Vietnamese (and succeeded in killing a large percentage of those who lived in Cambodia as well as about 100,000 Muslim Chams), but this was clearly a ludicrous ambition, the equivalent of the Belgians trying to eradicate every last German. Rwanda is an interesting case. Many would claim that the differences between the Tutsis and the Hutus are not racial but class-based, between pastoralists and agriculturalists (IIRC). Which makes an interesting dilemma: if it was class-based rather than race-based mass murder, does this make the events of 1994 somehow less evil?
I think you and I would probably not have too different an estimation of the crimes of various Communist parties around the world. I don't know if you've read it, but Rudolf Hoess (not Hess), the commandant of Auschwitz, wrote a kind of memoir while awaiting execution, attempting to explain what the Nazis did and also to justify himself and to diminish his own guilt (didn't quite work out that way). One of the things he wrote about was the eagerness with which they visited captured Soviet gulags, which they understood could be used to eliminate whole classes or races of people. I think Hoess expressed some mild disappointment at how barbaric (read inefficient) the Soviet camps turned out to be.
To put not too fine a point on it, I think one can find enough parallels between the Holocaust and other episodes of mass murder to say, "see, there's nothing unique here." (For example, Stalin labeled the Kulaks vermin...) Yet for various reasons, I tend to regard the Holocaust as something unique, a purer form of evil, perhaps.
I wonder if you agree with this.
Hmm, I probably would agree with you and Robert Conquest there, without being able to put my finger on quite why. To use an analogy, I'd say the Holocaust was absolute zero, minus 273 degrees centigrade, but that the efforts of Stalin, Mao, Pol Pot et al. were only slightly less chilly in the low minus 270s. Actually, the attempt to compare Pol Pot to Hitler has been used for dubious ends in an attempt to deflect attention away from the fact he belonged to the Far Left, rather than Far Right, tradition of mass murder. As William Shawcross pointed out in his obituary of the Cambodian dictator, the notorious Khmer Rouge detention centre Tuol Sleng (S21) resembled the Lyubyanka rather than Auschwitz (although I think the Khmer Rouge did reach one of human history's moral lows by converting the entire country into one huge concentration camp, where everybody was either a prisoner or a guard). Democratic Kampuchea is evidence of what Piotr Rawicz called Nazism's one great superiority over Communism: it ended in 1945.
I think this is one of those things that you feel in your guts.