You see, communism, in theory, is great. The biggest problem is that it requires a benevolent authority to determine what is provided based on what is needed and wanted.
This is a problem because usually communist countries are structured at authoritarian, where the head of state, a person, usually some guy, is in charge of such things, generally with the help of those in the government. Being human and innately flawed and selfish, all communist systems thus far, seem to follow the same trend of exploitation and indentured servitude for the majority of the populous, meanwhile the "upper class", mainly the elite and the person's that make up the government live in luxury. More for them and the bare minimum for everyone else.
If this human factor problem could be resolved, then communism would be a great system. Everyone shares in the wealth and success of their countrymen. But since people are the cornerstone of any government, the system will always be prone to exploitation of the people.
As for Stalin specifically, I don't see him or his actions as notably different than any other communist dictator. They are all equally terrible people for very different human rights crimes.
I like the idea of communism, but I wouldn't trust any single person to be in charge.... I wouldn't even trust a coalition of people to run it. It would need the involvement of enough people from the population from all different walks of life to essentially vote on policy changes constantly in order to ensure that no individual or group of individuals is unfairly benefiting from the situation, which, that, in and of itself, would be a nightmare to try to put together, manage, coordinate, and abide by.
Capitalism under democracy isn't a picnic, but at least there's enough responsibility imposed on the system by the population that is being governed, that any exploitation is generally slowed at least, or eliminated at best (often the former and not the latter).