The level of psychopathic aggression that Nazism showed really wasn't comparable to anything in the Soviet toolkit. They were never that aggressive-slash-insane, and they could be trusted to a point (maybe don't send them your gold reserves).
It's the lack of higher ideals plus the glorification of amoral violence for its own sake as an aesthetic standard that made Nazism so repugnant and so dangerous.
@Bookmark1995 @GOU Limiting Factor I agree with both of you, and wish to add my two-pence on this train of thought. Even at their worst (and I am as far from an apologist for Communism or the Soviet Union as you can get), the Soviets were rational. There was some logic of statecraft behind their actions, even as immoral and heinous as they were. The ultimate goals and endgame for Soviet interests were based in reality more often than not.
The same could never be said in any fashion whatsoever for Nazism. It was probably the most "successful" death cult to have ever taken power. By that, I don't just mean its incredible ruthlessness or cravenness, but the very heart of its doctrine and reason for being was the stuff of nightmares, and no mountain of bodies or burned-down countries would've been enough for the Third Reich as long as it lived. And considering how short a time it was on this Earth, that's saying something.
Let's not kid ourselves: Stalin under the USSR was still terrible. And little better then Hitler in many, many ways.
Stalin indulged in a bit of the ol'ethnic cleansing: his starvation of Ukrainians, the deportation of the Caucasus peoples, the deportation of the Crimean Tatars, persecution of the Volga Germans, persecution of the Poles.
His secret police man was a vile serial killer and rapist.
He butchered his own military, his associates, and many others who helped put the Bolsheviks in power in the first place.
He had zero tolerance for other competing left-wing ideologies. He screwed the Spanish anarchists, calling them "fascist fellow" travelers, and tried to murder Tito for being the one communist leader not under his thumb.
And, had he not died, he would have unleashed his own purge on the Jewish population.
The fact that Stalin could be a lesser evil speaks tojust how vile Nazism really was. That so many who despised Stalin willingly fought for him despite how utterly horrible he was is itself one of the tragedies of modern history.
Adding to this, the Holodomor, the Great Purge, and the Gulag Archipelago, as heinous as they were, were not reasons the Communist Party of the Soviet Union existed but were rather side-effects of Soviet Communism. For that matter, the Great Leap Forward and the Cultural Revolution were not reasons the Communist Party of China existed. Communism's crimes were bugs/side-effects of the ideology while Nazism's crimes were features of said ideology and reasons the Nazi Party existed.
To me, human agency is one of the things that really drives history. The individual choices one makes does influence the outcome of events.
It wasn't evitable that the 20th century communist experience turned out so rotten. It wasn't inevitable that socialist came to be associated with famines and gulags.
But Nazism was, at its core, an ideology that brooked no human decency whatsoever. As soon as Hitler died TTL, one of his acolytes would not only continue his wretched war, but unleash new horrors, like the destruction of Paris.
Nazism, had it lasted long, would've be the worst scourge since Genghis Kahn.
Reading this makes me thank God that Nazism died out over 70 years ago.