An argument I’ve seen is that we haven’t seen a truly communist country yet. The most promising ones (imo) were smaller countries who’s communist ambitions were stifled by American-backed coups. Many of the earlier communist leaders like Lenin and Mao also knew that their countries weren’t communist in practice, as you can’t slip a switch and suddenly you have working communism. Their goals were to establish governments that could lead their populations to eventually being communism in practice instead of just as an ideal. Obviously, this depends on having a government that is actively trying to make itself obsolete, and most politicians don’t want that.

Capitalism may “work”, but it’s definitely not sustainable without checks and balances and limits on wealth accumulation and influence. Allowed to roam free, it’s disingenuous to say they “aren’t perfect”, they’re destroying the planet and its people.