When you say "It only works on paper", the usual implication is "It only works on paper, because it's failed every time that it's been attempted" even if you coach it in language like "human nature". But if the reason that communism has always failed in real life is that the US has tried to stop it from succeeding, that really says little about the hypothetical success of that system.
It'd be like if I said to you that bars "just don't work" in my hometown, because they always lasted a month before having to close due to lack of business, but disregarded the fact that I regularly firebombed bars in my hometown.
Except that's just post hoc bullshit peddled by literal communists who refuse to accept that the communist experiments in the 1900s were catastrophic failures.
As we'd expect from an incoherent and violent workldview from the 1800s. ---