To my knowledge, none of these instances involve a government slaughtering people that they considered to be "their own." These massacres were perpetrated against some "other" that they had convinced themselves was the enemy or in some way inhuman. PM Green orchestrated the deaths of what were, ostensibly, his own people. In historical terms, this might make him even more horrific than Hitler and perhaps on par with Stalin or Pol Pot.
Personally, I don't share your grim assessment of humanity. I think it takes a special kind of monster to conceive the plans for an orderly genocide.
Many of those put to death by the Nazis were German citizens, they might have been defined as others as you put it, by virtue of being Jewish, but they were still German. By the same token Green was picking an other too; the underachieving, the underclass whatever you want to call it. He was using a justification to discreminate against his own the same as Hitler did. To suggest Green is somehow worst than Pol Pot, Mao, Hitler, Stalin, Mugabe etc makes little sense. They all killed 'their own' in one way or another.
Green is certainly in a different class than some of those, I'll grant. Still, Green never made any open statement that he was selecting certain children because they were an "other." On the contrary, under any other circumstances, he would embrace their patronage. Which is more monstrous? To order the systematic executions of people that even you consider to be innocents? Or to plot the genocide of a race that your diseased brain considers unfit to live?
But ultimately, in the case of PM Green, I think Pol Pot is the most apt comparison. Pol Pot slaughtered many of his own people in the process of "reeducating" them for "their own good."
I like to think I have a realistic assesment of humanity. As a species we are capable of the most base horrors, but also of truly wonderful kindness and sacrifice.
I'd agree that humans are capable of reverting to brutal tactics (or at least turning a blind eye to them) in the name of survival. However, I think very few people are so bereft of morality that they could be the central architect of such an injustice. "As a species," I don't think we can make that kind of generalization. I could never plan an arbitrary genocide. I hope to god you're not saying that you are capable of such a thing.
Well personally I'd query whether anyone deserved to be tortured? Torture is rarely an effective intelligence gathering tool and, quite frankly, even if it were it is surely barbaric and something that all people who claim to be civilised should abhor (no matter what Jack Bauer says).
You're dealing with 3 different questions here:
1.) Does anyone deserve to be tortured?
2.) Is torture effective?
3.) Does torture morally harm the people who perpetrate it or sanction it?
My answers:
1.) Yes, there are, at least theoretically, people in this world who are such absolute bastards that they deserve to be tortured. (However, I'd speculate that only God really knows who those people are.)
2.) I'm not sure, though I'd wager usually not. Ironically, torture would probably be most effective against those who didn't deserve it.
3.) I don't know. Probably only if you're torturing people that don't deserve it. (That's not to say that torture doesn't psychologically harm the people who perpetrate it or that it can severely damage the soft power of a nation that employs it.)
["The Moral High Ground" is] The ability to turn around to your opponant and say we are better than you because we won't torture our enemies, we won't rape their wives or eat their children.
Well, I've never been arguing from a position of personal moral superiority. I'm as flawed as any man. I don't expect anyone to agree with me because I'm a good guy. I expect people to be swayed by the justness of the arguments.
As I've said before. If there were a virulant plague, and the government (any government) did not have the vaccine for eveyone, then any government will make decisions over who gets it and who doesn't.
And as I've said before, this is an inaccurate analogy. There is a difference between a government trying and failing to allocate a precious resource to all of society and a government selecting specific individuals to die for the good of society. A more apt anology would be this: Suppose, in order to create this vaccine that will save billions of people, they first needed 100,000 people on which to perform fatal medical experiments.
Regardless of how great the needs of the state are, they cannot possibly trump an individual's inalienable right to life & liberty. No government can have this kind of authority over its citizens and any government that does is unjust.
My initial gut feeling would be no I wouldn't, however I don't think any of us can truly know what we would do in such a situation until the chips were actually down. 
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