It's not even an issue of population. Communism requires material conditions you simply cannot create by killing the opposition, no matter how much you desire to preserve "the revolution."

Capitalism is but one manifestation of material and labor scarcity. Until those things are eliminated you will experience the exact same ills in one form or another. Until those things are eliminated the only option available is harm reduction. Revolutionary communism fails specifically because it fails to recognize itself as a particularly shitty form of harm reduction, insisting the entire concept is bourgeoise propaganda. This is what contemporary leftist theorists have come understand, and what obnoxious internet edgelords refuse to acknowledge, because it requires admitting that Stalin and Mao didn't get it right.

Ironically this is literally the foundation of Dengism and modern China, which MLs say they like, until you reduce it to first principles, at which point it once again becomes bourgeoise propaganda.