If anything, it’s more worthwhile to engage with theory noobs vaguely sympathetic to communism than it is to waste time on confirmed anticommunists. Usually when the latter try to ‘debate’ with me, I reply with ‘Good point. You really showed me how wrong I was. I wish that I were as smart as you.’ which is my more polite alternative to saying ‘fuck off’. Any debate where somebody’s goal is ‘winning’ is not a debate worth having.
Now theory noobs, on the other hand, those people are worth engaging. Judging by their futile arguments with capitalist apologists, they’re already more‐or‐less sympathetic to communism, or at least ‘the idea of it’, so the door’s unlocked for you. The problem is that their politics are very undeveloped: they can’t explain why the people’s republics resorted to ‘authoritarian’ measures, or how they were better than the anticommunist régimes that preceded them, or even why they existed at all, so they resort to crude shortcuts like ‘well, those states weren’t socialist’ (which may indeed be true, but it’s a dull counterargument that gets us nowhere).
That’s where you can come in. Politely correcting them or expanding on their points is going to develop them more than any argument with a capitalist apologist ever could. More than likely, you’ll be introducing brand new information to these people, and that will hold their interest. I vaguely remember (possibly misinterpreted) a documentary that discussed Imperial Russia and hyperinflation. When I learned about the defects of Imperial Russia, the turn to Bolshevism was suddenly much easier to understand, even if I still didn’t quite agree with it.
Act natural. Don’t overwhelm them with too many resources (link spam) or paragraphs at once. If they ask why you approached them and not the anticommunists that they were trying to debate, you can reply with ‘Because I know that you’ll listen.’