I gave my self a brain aneurism reading the comment section of a COD video on YouTube. I came very close to replying to a bunch of people, but it just felt futile. You would have to unpack so much propaganda, cover so much history, explain dialectical materialism etc. to even get them to consider that maybe communism or the USSR weren't pure evil.
Maybe it would set one or two people down the road to questioning things, but it's just not worth that kind of effort. Starting to feel like the only way to convince people in a way that matters and is effective is to have socialist organizations in their lives that are positive and then the receptiveness of explaining those types of things to them will be much greater than just one comment on an internet thread.
You already said it yourself, I think. In marxism, the "base" is everything that has to with the material conditions of society, labour, production, wages, etc. "Superstructure" are all the formal, legal, cultural sides that follow from that. The relation between the two can obviously be complex, but in a marxist analysis the base will be dominant. And that's why political action is best rooted in real life, material problems - based, so to speak.