We as humans can often be found imaging an ideal world or nation in which we would like to live, where there are no problems that persist. An important factor would be the type of economic system in which you have since it is a classification of the reality in which society lives, with the most common ones being Communism and Capitalism. The idea of communism typically tends to fail for several reasons and this is backed up by historical evidence. For starters, communism is a far-left wing ideology and some of the main principles include no private ownership, shared property, and an economy run by the people. In the United States, we adhere to Capitalism which is the complete opposite of Communism. Capitalism is an economic and political system in which a country's trade by private owners for profit, rather than by the state. Communists perfected concentration camps while Hitler was in jail in Germany. Communists put Ukrainians, Kalmyks, Cossacks, Chechens, Lithuanians, Poles, and many more ethnic groups in concentration camps before Hitler. Stalin and Lenin repeatedly starved out and deported groups based on ethnicity until they submitted to cultural destruction and assimilation like the Cossacks, Ukrainians, Volga Germans, many many more. This was easy from communist philosophy since communists believe in class genocide, all they had to do was associate ethnicity with a class enemy like nationalists or in the case of the Cossacks, their association with the Tsarist elite army units. It didn't matter if you were Tsarist, you were part of that group and deserved forced labor and extermination for your collective crimes. This was not entirely different than why Hitler rationalized the extermination of the Jews. He thought they were the top bankers, businessmen, and financiers that ran the capitalist, communist, and most of the socialist organizations. Hitler was a socialist and hated capitalism. How exactly was Stalin bad from a communist perspective? The idea that Lenin didn't like Stalin is conflicted in the sources but even if so Lenin was no different. To understand Stalin we must understand Lenin. He recognized that to create a stateless Marxist utopia, the communist proletariat dictatorship must wield power to seize the means of production and wipe out all opposition. Lenin noted that the liberal democratic way was useless and an obstacle rife for subversion. Once all opposition was destroyed, the dialectic would "naturally" evolve into the utopia. That is where Stalin comes in and Trotsky. Both of which ordered and took part in the murder of millions. No matter who came to power the result would have been the same. They used state dictatorship as a means to an end by any means necessary. How exactly is that contradictory to communism? Lenin's best man was Dzerzhinsky who certainly was no different (just another delusional criminal maniac in power to destroy any opposition). Lenin proceeded to label starving Union workers (Unionists), moderate socialists (Mensheviks, Social Democrats, many others), and anyone who disagreed with him as speculators, saboteurs, counterrevolutionaries, etc and killed untold many of them. Those who were late or didn't work long or hard enough were shot because they weren't "revolutionary enough. Communism has been tried in Europe, Asia, Africa, and the Americas and everywhere it failed and left 100+ million dead following the same principles in completely different cultures. The failure and tyranny of communism are self-evident. Only obfuscation, ignorance and resentment keep it going. In the USSR there have been 20 million deaths as a result, along with 65 million deaths in China, 1 million in Vietnam and the Warsaw Pact, 2 million in North Korea and Cambodia, 1.7 million deaths in Africa, and 1.5 million deaths in Afghanistan. As you can see, communism produces super inefficient economies, and even though the people in a Communist system fully support its ideals, they soon start conducting themselves in a manner that shows their desire for the freedoms of Capitalism.
Communist Manifesto by Karl Marx: https://www.marxists.org/archive/marx/works/sw/course/mscp.pdf
Critical Companion to Contemporary Marxism: https://www.ssc.wisc.edu/~wright/621-2013/CRITICAL_COMPANION_TO_CONTEMPORARY_MARXISM.pdf
Soviet repressions of Polish citizens (1939–1946): https://en.wikipedia.org/wiki/Soviet_repressions_of_Polish_citizens_(1939%E2%80%931946)
Times of Israel: https://www.timesofisrael.com/how-hitler-used-jews-failed-wwi-era-idealism-to-feed-the-worlds-worst-genocide/
The Bolsheviks: https://www.marxists.org/subject/bolsheviks/index.htm
The Black Book of Communism: http://www.jrbooksonline.com/PDF_Books/blackbookcommunism.pdf