I feel like talking about Stalin is like walking on eggshells... You don't want to go, "Stalin's death toll is overexaggerated, in my opinion he didn't kill enough people!!!" because that will make the average person instantly stop hearing you
What's the best way to talk about Stalin in a sensitive way that doesn't trigger a fight or flight response?
I like to point out that the USSR did the bulk of the fighting in defeating Nazi Germany. That alone doesn't intrinsically mean the USSR was good (technically one shitty power can fight another, like when the US starts fighting Imperial Japan), but if somebody believes the Nazis were terrible as they should and as is common among western liberals, then positioning the USSR as the actual savior in that equation seems like a step up from the aggrandized contributions of the western allied states, especially the US who comes in at the tail end and acts like it always hated Nazis. Even though it continued to work with them after the war, even though the Nazis modeled their discriminatory policies after Jim Crow laws, etc.
It's not a direct point about Stalin, but he was the one at the helm during that period and certainly played a part in ensuring the USSR was more than ready when Nazi Germany attacked.
In other words, if somebody is very entrenched, sometimes a good starting point is springboarding off of what they already believe. "You think Nazis are bad? Good! Here's the guy who headed up the state that destroyed them." "You're a Christian and believe in the teachings of Jesus? What about when Jesus said 'I was hungry and you gave me to eat.'?" "You believe in the sanctity of life? Then what's up with the US murdering kids in another country, huh?" And so on.