Marxism leads necessarily and unequivocally, with scientific precision to genocide at worst or to misery at best.
Besides any opinion, any expectation, that is just plain historical fact. Marxists appeal to the "no true scottsman" fallacy every time this is pointed out to them. If you compare with any other ideology, Christianity as a social phenomena for example, you clearly see different results humane governmnets, cruel ones, competent, incompetent, just about every variation of it. Same goes for democracies, monarchies and so on.
With marxism every single time it was explicitily used as the only source for statecraft it led to destruction. If any doubt remains we do have scientific controls over that: East Germany. West Germany; North Korea, South Korea; Hong Kong and Singapore, China; all cases where more or less the same people, same culture, same history, where marxism was applied in one half and some other system was applied in another half, marxism consistently killed and created misery and you had people trying to escape the marxist side to the non-marxist side. Another interesting case is Puerto Rico and Cuba. A common accusation from marxists is that the US is an imperialistic force that wants to neo-colonize other countries. Cuba is a beacon of this "resistence" while Puerto Rico is for, all purposes, effectively a colony. Who is better off? One can clearly see that American imperialism is not imperialism in the classic sense. It's just commercial hegemony which is far better then actual imperialism. I always find it beautiful how some radicals think that McDonnald's creating jobs locally is an offense that demands paramilitary armed reaction or protests from spoiled children who used to go there when younger and now think that Ronald is the new Hitler. Yet, when we see an actual collony of the US, collony in the classic sense, you find out it is a far better place then Cuba, the marxists Island of Fantasy. When Brazil got independent in the 19th century, two African countries actually asked to be our collonies (the emperor refused). I bet that a c ouple of them would ask the same if they saw how "evil" the US is to its real collonies.
That is the empirical facts. Now a bit of theory that shows why Marxism necessarily leads to mass destruction. Marxism basically defends that the radicalization of Capitalism should naturally lead to Socialism. That’s why since the 19th century Marxists have been writing “Crisis of Capitalism” books which keep coming out of the press with the same obstinate steadiness that millennial predictions of the Second Coming are produced. And the sect goes on even after their predictions fail. True believers of Marxism are always waiting for the “Great Coming” of the Socialist society to arise from the ruins of capitalism. When it doesn’t happen some decide to take into their own hands the process in several forms of social engineering which include the control over the oppressors of society – the culprits who prevent the emergence of the socialist society. Now, there are real oppressors in society, in politics, in economy, in religion and so on. These are powerful people who would do anything for power, money and prestige. They are powerful and dangerous, real predators. The Left then decides that it will not simply take reaction against them under due process. They decide they have to destroy oppression in all its forms and expressions, even in a preventive way. To do that they must, whether they are aware of it or not at the beginning, become stronger, richer and have more prestige then all the oppressors put together. Thus, the typical centralization of power that the left has produced. Now when a group of men has such monopoly of sheer secular power in any society or country, the consequences can’t be but lethally devastating. I am not saying that being a leftist is the only thing that leads some groups to such centralization of power. But surely, leftists cannot achieve what they want without it. That’s why they must fight every other source of authority in society that is not themselves: wealth, family authority, tradition, religion, everything, after all they are up against all oppressors in all areas everywhere and they have to be stronger then they all together. There can be no authority but their enlightened dreams. With such power always comes genocide and misery, which has already been demonstrated. Communism, Marxism, Socialism, should all be right there with Nazism as the collective social diseases they are and in the trash bin of History.