It’s extremely unconvincing to say “Sure it was horrible last time, but next time it’ll be different.” Trotskyists and ultraleftists compensate by prettying up their picture of socialism and picking more obscure (usually short-lived) experiments to uphold as the real deal. But this just gives ammunition to those who say “Socialism doesn’t work” or “Socialism is a utopian fantasy.” And lurking behind the whole conversation is Stalin, who for the average Westerner represents the unadvisability of trying to radically change the world at all. No matter how much you insist that your thing isn’t Stalinist, the specter of Stalin is still going to affect how people think about (any form of) socialism — tankies have decided that there is no getting around the problem of addressing Stalin’s legacy. That legacy, as it stands, at least in Western public opinion (they feel differently about him in other parts of the world), is largely the product of Cold War propaganda.
That’s the gist. Then he goes on with another paragraph of whataboutism but of course not a single mention of the tens of millions of dead both, Stalin and Mao, were responsible for.