Ok, now I actually have time to post a full statement (the other two were written in the span of ~15s each).
Communism has two fundamental problems: its totalitarian and socialist. Both are bad.
Totalitarianism represents the ultimate failing of government: an absolute failure to trust its citizens to be able to lead their own lives. Government controls everything; the official government line is the truth, and anything that remotely contradicts this propaganda is repressed. I mean, the Catholic Church made Gallileo repent for a great advancement to scientific though; imagine what would happen to more fundamental advances (read: particle physics) especially in a totalitarian society with a government-endorsed religion. In the same vein, education will almost inevitably consist largely of government propaganda so as to indoctrinate children early. Loom at Mao: kids were told ad nauseam that Mao was the ****, and that to go against the government was inherently wrong, because the government was inherently not. With all of these intellectual constraints, very little progress can be made, etc.
Socialism is just fundamentally stupid; it goes against basic human nature. No large group of people will ever agree to absolute economic equality, and for good reason: it cannot work. If you're automatically receiving the same government-issued paycheck as everyone else, why should you attempt to work? The lack of competition, especially when coupled with the intellectual stifling that accompanies totalitarianism, invariably breeds a lack of innovation, with therefore leads to economic downfall for the entire country.
So no, I'm not just trolling, I didn't have time to write out a full post.