Back to the Holocaust:
For my previous comments on the Holocaust (prompted by David Bernstein's post on Mel Gibson), see post #1 and post #2.

Lynn B. at InContext was "simmering" after my first post; but in her update (after my second post) she says that she still disagrees but now understands where I'm coming from, and promises a possible future post where she goes into greater detail. She also points to a post by Meryl Yourish, so let's go there. Meryl says (formatting retained but links omitted):

Its uniqueness was due to the fact that a nation set out to exterminate all the people in a certain ethnic group, all over the world. Hitler started with the Jews of Europe, and did an astonishingly thorough job. His goal was to continue until the entire planet was judenrein. He didn't "just" kill a lot of Jews. He created an efficient, organized death machine whose purpose was to eliminate Jews from the planet. It wasn't just mass murder. Its purpose was the extinction of the Jews. Exctinction. Let me say that one more time: The extinction of the Jews. Had he succeeded in Russia, Sasha, neither you nor your brother would be alive to blog today. Had he defeated the United States, then I wouldn't be alive to write this today.

Another aspect of the uniqueness of the Holocaust is that many of the nations which Hitler conquered were willingly complicit, helping to round up Jews and ship them off to the camps. They, too, wanted to see a world without Jews. No such thing happened in any of the other atrocities you mention. Pol Pot wasn't aided by Korea and Thailand. Stalin didn't have help from China. Hitler had his adherents in eastern Europe, even in Poland. Read the stories of Holocaust survivors. Polish Jews were massacred by the Poles while under German rule. Half the world was complicit in this, Clayton. That's why it remains emphasized. Not because Jews control the U.S. media. Because the world let it happen.

As Lynn pointed out, this isn't a question of which killing is greater than which. It's the concept of the elimination of an entire people from the face of the earth. In his attempt to eliminate world Jewry, Hitler destroyed two-thirds of the Jewish population of Europe. The amorality of it isn't in the killings, Sasha. The amorality of it is in the attempt to eliminate an entire people from the face of the earth. That is the Holocaust's moral uniqueness, and that is what you should "believe" in. Yes, Stalin killed more Russians. But Stalin wasn't trying to eliminate all Russians from existence. There was no "Final Solution" for him, or for Pol Pot, or for some grisly serial killer.

So it's the purpose that makes the Holocaust specially evil, according to Meryl: setting out to kill every single Jew, and succeeding in killing six million, is morally worse than setting out to kill an equivalent number of random people, and succeeding in killing six million.

Alas, I still don't buy the moral uniqueness. To repeat my point from below: the Holocaust is evil because killing six million Jews is six million murders, and committing six million murders is highly, highly evil. Really evil. But not more evil than killing six million other innocents. (As I've mentioned below, the Holocaust also has lots of characteristics that make it especially grisly, especially memorable, especially important as a cautionary tale, especially relevant in a world of ethnic warfare, etc.; but you can be all those things without having extra evil.)

Take any six million people murdered. You can draw a circle around them and say, "These six million people define a particular group X," and the killing of these people is especially evil because it's the systematic extermination of everyone in group X. Of course, in the general case, there's nothing "special" about group X. It's just a somewhat random assortment of people: {Fred, Dave, Sasha, ...}. Why should the set Y = {Jews} be "special"? Only because there's something special about having Jews in the world. But "an entire people" has no moral value, except insofar as that "people" contains people. I don't care whether Jews as a group exist; but I do care about every individual Jew, as much as I care about every individual whatever-else. Corollary: Every group X containing six million people is equally valuable, and any murder of any group X is equally immoral.

Tangential note: I've gotten some e-mails saying that the Holocaust is 11 million dead people, of whom 6 million were Jews. I don't know what the canonical definition of "Holocaust" is; Merriam-Webster says it's the slaughter of "European civilians, especially Jews"; whatever it is, I'm just sticking with the Jews because it's the Jewish part of it that people tend to claim is morally unique.

Second note, on complicity: In Meryl's post, I'm not sure what work the complicity of other nations is doing for you. That just makes it a mass murder with lots of responsible parties. More people to punish, perhaps, but having lots of participants doesn't make an act more evil.

Third note, on intent and criminal law: Several correspondents have noted that not all killings are created equal: after all, in criminal law, we do distinguish between different kinds of killings, based on intent. True enough, but if we're going to rely on intuitions culled from criminal law, those intuitions actually favor my view. "Intent" is a very particular animal: in the words of Glanville Williams, "A consequence is intended when it is desired to follow as the result of the actor's conduct." I've got a gun, I knowingly point it at you and pull the trigger, knowing that you'll probably die as a result and desiring that you die -- that's murder. Did I do it for money? For sex? To eat you? Because I hate Jews? Those sorts of motivations are irrelevant to whether it was murder.

Now, motive isn't always irrelevant in criminal law: see, e.g., crimes defined in terms of doing an act with some further intention; defenses based on the rationale of justification (like self-defense); whether disconnecting someone from a life-support system is considered a mere (non-criminal) omission or culpable homicide; and "hate crimes" (where such a statute exists). And motive is usually considered relevant to sentence. See generally Kadish & Schulhofer, Criminal Law and Its Processes 214-15 (6th ed. 1995) (citing useful sources). But many of the above are properly viewed as exceptions, not the general rule; "hate crimes" and the like are highly controversial (and I'm not a fan of such laws); you can justify self-defense without having recourse to motive; and sentencing is based on a lot more than just how evil the act is, so differences in sentencing doesn't necessarily imply a different intuition about the evil of the act.

In short -- while it's not clear that the actual practice of criminal law should have any moral weight -- if you're going to use the criminal law in this debate, most of it doesn't support the idea that racially motivated mass murder is worse than any other mass murder.