Please don't conflate tankies with leftist thought. They are not leftists. They are fascists with strong ties toward fascist regimes that are "known" to actively usurp elections around the globe.
A good metric is: a very hardline Communist might have an argument for why effectively slavery is ethical because social and economic planning requires people to engage in jobs they actively do not want to do. I personally consider that the reason that Communism can never work at scale but that is a discussion that needs to be had.
A tankie will just justify anything that China or Russia do. Usually with an attempt to deflect by pointing out something the US or, increasingly, certain EU countries did.
But, regardless: There is another issue with your "just let everyone taolk it out" nonsense. Because the ml moderation team(s) and admin staff have increasingly been using mass bans and false claims of xenophiobia to shut down anything that is not tankie bullshit. So there is no discussion. Just one sided propaganda in some of the largest communities on lemmy.
To expand on the moderation strategy a bit. A LOT of people who aren't increasingly of one nationality and ethnicity have a lot of problems with ResetEra's moderation strategy. The mods and admins are known for using a heavy hand and outright mockery against anyone who they disagree with and the remaining community stumble over each other to be part of the "cool crowd".
But you can also very easily see why the vast majority of leftists and PC gamers and... Asian people left. Because they have a policy to only edit user posts when they contain actively dangerous/illegal statements. So you can see when someone catches a permaban because they dsiagreed with an admin or joked about the corporate interests behind brexit. And you can see the discussion of the remaining users on why that was so fucked... up until the thread gets permanently locked.
With the model ml (and certain other more "world"ly instances...) use... you don't. You just see comment branches disappear the moment anyone pushes back on some propaganda. And if a user pisses off the admins, they get banned straight up. Often with some comment about how they are racist or xenophobic in the modlog with all of their comments removed but NOT in the modlog. And that is a problem because, unless you were actively following along with that discussion, you never see anything other than MAYBE "wow, a lot of really racist people disagree with this very smart discussion on why Chinese Taipei was always a part of China and is totally not a sovereign-ish nation called Taiwan"