Communism clearly advances human flourishing, in Marx’s view.
This is central. We believe that what capitalism began, in its finding a way to produce so many means of production–the construction of material abundance–must now be completed through socialism. That capitalism did create good in some ways / from some perspectives. But that something else has been trying to break through just as bourgeois democratic republics and capitalism broke through monarchy and feudalism. The communist movement is a trans-historic phenomenon, of the same if not greater world-historical significance than capitalism. The drama between capitalism and communism is probably built into nature in that it probably (in my opinion) occurs in many if not most intelligent species that evolve in the universe.
Liberals would be communists if they realized that we can be most liberal under communism.
Libertarians would be communists if they realized how much freer each soul is and all souls are collectively under communism.
Conservatives would be communists if they realized that the morality they’re trying to preserve can be most fully and beautifully realized under communism.