Edit: oops I thought you wrote ancap but like 50% of this still applies. Just replace "markets" and "competition" with "we'd figure it out through affinity groups and some sacrifices are just worth it", the latter inevitably beginning genocidal/eugenicist in its implications.

Every "ideology" in that vein is based on short-term idealism. They have absolutely no idea what they'd actually do with power, and it would immediately collapse into liberalism (or similar) because the economic base would remain identical. They think they can change the base purely through minor superstructural adjustments.

Any attempt to realize their vision would result in gangs and black markets that eventually collude to hash things out legally rather than in the streets, keeping out small players through financial largesse, as liberalism is much cheaper than gang warfare. Any time you mention this, they will resort to a pure idealism premised on nearly everyone instantly becoming a deeply committed rule follower (the rules are the morals they teach each other) and market knower. Monopolies? Oh the "free market" automatically solves them, like magic. "Competition" automatically always happens even though monopolies are the inevitable antithesis of this and work directly against it using the mechanisms inherent to capitalism. The issue of natural monopolies is basically just ignored, they can't even think about the nonsense that would be implied from having, say, 10 different street network companies somehow competing with each other. They just retreat to "they'd figure it out. Markets. Competition. Marginal value. Abolish age of consent".