For the record, the claim that Marxism fails because and only because men are selfish is absurd.
Earlier communists, such as Gracchus Babeuf, thought greed caused all other sins and social ills, and that the elimination of private property would eliminate greed hence eliminate all sins and social ills, and re-create Eden before the Fall. Marx followed this idea and went further, saying man are shaped by their institutions, so that evolving their institutions evolve man.
He envisions a New Jerusalem, where human nature evolves into a "species being" where all men are one collective hive mind where individuals are sacrificed selflessly to the needs of the hive, selflessly, without hesitation. (Please see THE SCREWTAPE LETTERS for a find depiction of a hell where all men consume and absorb each other's lives in an endless vampire feast.)
But Marxism does not fail because men are sinful or selfish. Marxism fails because it must.
Even with elves or angels, moon-men or robots or any other kind of being imaginable, Marxism cannot work:
1. By design, Marxism rewards unproductive behavior and deters productive behavior. This means all a Marxist run commonwealth can produce over time is unproductive behavior.
2. Marxism promises that changing laws and customs will eliminate scarcity of resources, opportunity costs, time-preference, disutility of labor, and the limited utility of factors of production. But these things are factors of reality, independent of human nature.
Even Adam in Eden before the Fall had gardening to do, and even he cannot dig a well in the same spot at the same time he plants a fruit tree.