any system could be free enough of flaws to be above criticism- or that it's good enough to be worth the oppression of the few without hearing their voices and honestly considering their plight.

I don't think there's many MLs that would argue against you here, at least as far as ideals go. In fact you'll find a lot of internal criticism of past socialist experiments. It's just not really criticism if it's not taking into account historical context and/or if it's based largely on western misinformation.

What most western criticism of AES lacks is key historical context (this comment is very stream of consciousness so forgive me for being all over the place):

Threats of invasion, sabotage, espionage, assassination, etc have always been a threat to vested power, but even more so against revolutionary movements. Rosa Luxembourg was killed. Lenin was nearly assassinated (may have caused him to die early). Stalin may have been assassinated. Castro somehow survived hundreds of attempts and plans. Che was killed. Allende was overthrown (and maybe killed). Árbenz was overthrown. Malcolm X was killed. Fred Hampton was killed. Sukarno was overthrown. Sankara was killed. All this just off the top of my head, there's plenty more examples.

The Soviet Union had 20 years to somehow industrialize well enough to face European invasion, withstanding both internal and external attacks. The alternative was quite literally death.

The absolute strength, size, and resources of the US empire are unprecedented, which significantly alters the material conditions and thus the strategies that must be employed by revolutionary movements for survival. US intelligence agencies have become very good at manufacturing or manipulating social unrest to destabilize a country and set up a coup. Check out The Jakarta Method for an overview of some of these strategies.

So yes, ideally we would all interact freely in the marketplace of ideas, and bad ideas would be refuted by facts and logic. But the unfortunate reality is that bad faith actors and saboteurs have proven incredibly effective at materially undermining revolutionary movements, and thus any criticism of those movements must take that into account or it's a useless criticism.