I think that people can get so caught up in left and right, politics, or ideological distinctions, that they miss crucial similarities. For example, maybe Stalin differed with Hitler on some esoteric political theory, but, both Hitler and Stalin could make anyone disappear in the middle of the night for no reason at all. That is one very important, overriding, similarity IMO.
Hitler and Stalin both invaded their neighbors. In one case, Poland, they divided the country between them. Hitler and Stalin both contributed to the deaths of millions of people, in concentration camps, in political prisons, on the battlefield, shot in secluded rooms, tortured to the end, or hung in public squares.
One difference is, of course, that some progressives in the United States defended Joseph Stalin. They claimed the purges were real trials, that there was no mass starvation in the Soviet Union. In 1956, when the information began to trickle out, it became difficult to deny what had really happened. Another difference is the continued viability of Marxist thought in the academy.
Do we have a propensity to scream “McCarthyism” when anyone analyzes Communism, in particular with respect to the history of espionage within the US? Now that we know there was far more spying than most people thought, how does that change things?
McCarthy was bad. But how do his excesses compare to Stalin? Given the bluster level you would think Joe (M) was worse than Joe (S) sometimes.
Check out the “Watch and Listen” video by the BBC. The young Russians seem to really fancy old Joe.