They may be gish galloping you:

Gish gallop (sometimes gish gallop or Gish/gish galloping) refers to a rhetorical technique or strategy by which a debater puts forth too many false arguments for their opponent to be able to refute in the allotted amount of time.

https://www.merriam-webster.com/slang/gish-gallop

The important thing to remember is that outside of strict debate club rules or something, there aren’t really any rules of debate. You aren’t obligated to respond to any given claim/point a person makes, much less take it seriously. Some people will try to use this against you, as in, “You’re ignoring what I said, you refuse to, blah blah” but too bad. They’re just trying to get you to adhere to an invisible scheme of debate rules that are to their advantage.

So for example, when they say “if communism is so great why did it fail everywhere”, you can shrug and continue to talk about ML ideas. Or you can go “idk what you’re talking about. anyway…” Or you can flip it around on them and go “according to what sources? the nazis? or perhaps the people who were barely through with owning slaves when they started saying communism is evil?”

In other words, set the terms you are willing to tolerate. People like this are leveraging talking points they (usually) don’t even understand that are designed to put you on the defensive for explaining things the average person would have a hard time being an expert in. So, figuratively speaking, recognize the CIA propagandist behind their words and argue with them rather than the propagandist.