Just remember, whenever you read, "social democracy is objectively the moderate wing of fascism," you are reading part of the justification for why the USSR should sign a treaty with Nazi Germany. The actual justifications for this are complicated, I think it is actually not completely straightforward such as "Nazis bad, treaty with Nazis make USSR fascist." However that is exactly the sort of campist and obscurative reasoning that Stalin tries to make. The argument was not "the USSR is still critically underdeveloped next to the most industrially advanced country in Europe, and we need some time to industrialize before we can oppose European fascism." It was, "The social democrats in Europe are worse than Nazis, so the Nazis need time to crush their moderate wing."
You can kind of understand the Real Politic of Stalin. It's the same justification for the endless purges of his political enemies. I think that the historical basis for authoritarianism extends beyond the "great man." But the guy was probably the greatest historical revisionist of the last 150 years. Both his enemy Leon Trotsky and his one-time secretary Reya Dunayevskaya meticulously documented how Stalin had history literally rewritten to make him seem like a more revolutionary figure than he was.
I recognize that Trotsky doesn't have a good rapport with anarchists, nor should he, after 1921. But If any leftist tradition "weighs like a nightmare on the minds of the living," it is the legacy Stalinism.