Communism sees competition as the root of all evils.
I guess Communists believe that a competitive environment would cause people and succeeding generations of these people to grow up greedy and aggressive so that competition would be the result of a vicious circle. Thus, over a few generations, a new circle might be set in motion, in which sharing and action on behalf of the whole population would replace greed and aggression as the basis of society and human character. Communists would therefore want to eliminate competition. But competition arises only when there is scarcity. So communists would, in order to eliminate competition, have to eliminate scarcity.