Communism is not socialism. What Stalin, Mao and Kim Il-sung did was wrong because they did basically the exact opposite of a socialist policy, centralizing power out of workers hands and taking all surplus value into the central government instead of distributing it.

They all turned into paranoid dictators who did everything they could to stay in power, except for Mao who got lied to by other party leaders and regretted it in his final years. None of them represent what socialism really is. Tankies who worship them are a small minority.