Aren’t people on ML instances also doing the exact same thing when they shout down and decry the wretched “liberals” (which seems to refer to anyone left-of-centre who doesn’t support communist party rule)?

Liberal is a well defined category though. Liberalism as a self-described ideology opposed to both communism and monarchy has been around for centuries at this point. Most people being decried as liberals would themselves identify as liberals.

The way political discussions are often policed on ML instances (This one, Lemmygrad, and Hexbear) is not conducive to helping new people see your point of view.

If you ask in earnest, you'll get good responses. A good number of people ask questions not to learn a different point of view, but to reinforce their own existing biases, which naturally becomes exhausting. Kind of like how POC get tired of justifying their existence to white supremacists, communists often for good reason get tired of trying to justify the existence of countries who choose to follow their own path, outside of the model of bourgeois democracy.

Aren’t people on ML instances also doing the exact same thing when they shout down and decry the wretched “liberals” (which seems to refer to anyone left-of-centre who doesn’t support communist party rule)? Whether it’s “tankie” or “liberal”, it only further entrenches the us vs them mindset.

Liberal, unlike tankie, has a fairly precise meaning in political discourse. It can be used too loosely IMO, but it generally means pro-capitalism, pro-individual freedom (including to exploit labor power to earn surplus value), pro free-market, pro-free speech (for all including reactionaries), pro wage-slavery, as well as specific limitations imposed on those considered outside of the "community of the free". Its important to realize that even the US mis-definition of liberal (as vaguely socially progressive) includes all of the above, and the internationally accepted definition of liberal, is right wing (for example, the right wing party in Australia is the liberal party). The best book I can recommend here, is Losurdo's Liberalism - A counter-history.

Not only that, but liberals rule most of the world, and especially most of the economies and governments of anglo-speaking countries, extracting a surplus from the sale of their labor power (who are mostly extremely poorly paid proletarians in the global south), and are responsible for most of the suffering of working-class people worldwide.