The Great Purge?
Of course, these people were selected for class and/or political reasons, not "racial" ones.
Somebody please explain to me why killing 6M "enemies of the people" is any less wicked than killing 6M "racial enemies of der volk."
Because Hitler vocally espoused a rival, socialist idealogy, railed against communists due to that rivalry, eventually betrayed and attacked the Soviets as a result, and the intellectual heirs of those communists have captured academia and the news media in most of the western world following WWII, writing the subsequent history and shaping popular opinion ever since.
That, and some deem class or religious belief mutable and therefore more escapable than race, as far as just who gets killed off. That somebody, in the millions or billions, gets killed off, is a given with such people. They're merely quibbling over the selection criteria.
Ugly, ain't it?
The Great Purge doesn’t compare, in my opinion. It was the same thing that happened in Cambodia later, but on a comparatively smaller scale than what the Khemer Rouge did. Just a bit more efficiently, due to the existence of Soviet bureaucracy.
I think you are making the mistake of thinking about this in the same mindset of critics of hate crime legislation (which is valid in that context). It isn’t that it was was somehow worse because they were Jews. It was worse because the state bent its penchant for efficiency in every single form to the task of genocide.
In the past, orders were given (or not) to eradicate people. Kill them on the spot, get them buried if you can, use whatever means at hand to accomplish your task.
The Nazis took their purported efficiency that made their autobahns great to drive on, their trains run on time, their institutions respected world wide and cradle to grave efficiency of documentation of their citizens, and bent those efficiencies to the task of genocide.
That is what made it different. Not because they were Jews. It could have been Catholics or anyone else.