Insulting or attacking other users, even so much saying "fuck you", "fuck [this group of people]", "you're an idiot" or anything like that while debating IS against the rules of Lemmy.ml. This goes for every political view, you DO NOT get free passes no matter if you're leftist, rightist, communist, anarchist, liberal, etc. If you're confident of your position you should be able to debate in a civil manner without cursing someone else out. I understand that debates can get heated and frustrating, hell I've debated with a good bunch of users, but you can still express that without resorting to name calling or insults.
Check the modlog, we HAVE removed replies of this nature from every political view, and even if we don't say it every time, we DO keep track of both removals per user and general behaviour even if it doesn't get removed, and too many infractions WILL result in a ban.
That said, it is NOT against the rules to present countering facts or opinions, or to have political opinions in general. Don't report comments for "being pro communist" or "being pro China" unless they have broken an actual rule, namely the ones about being civil. Don't attack or insult people from Lemmygrad just because they're from Lemmygrad or they're arguing for Marxism-Leninism or supporting a country you don't. If they're presenting their points in a civil manner (which had been the case for almost everyone from Lemmygrad), you can either read it and respond in kind with your questions or counterpoints, or just move on. People coming over from other instances is not brigading if they're mostly being civil, that's the whole point of federation.
Things people disagree with getting down voted is also acceptable, it's not considered an attack on you if your comment has a negative score, and it doesn't even significantly affect the ranking because of the relatively low comment volumes currently on Lemmy. It's just imaginary internet points, relax.
Most people from lemmygrad (and friends) will also insult you by calling you "imperialist" or "liberals", even though you clearly state you are not. I am anticapitalist and anarchist and receive these too often on Lemmy.ml
When various people are doing it to you, in small comments, it is not officially an insult but it's meant the same and it hurts the same. Plus some people are openly calling for this kind of brigading from lemmygrad users, and never receive a ban for it?
I'm grateful to the developers for providing Lemmy software, but you're not addressing the problem here, and it's hurting Lemmy as a serious alternative to Reddit.