Communism and Socialism aren’t inherently bad, as many seem to think. In fact, I would say that “true” Communism would be ideal. It would mean equality of everything. From my understanding, the problem with Communism historically is that it’s applied more as pseudo-Communism; or some other form of government in the guide of Communism.
Socialism is a fairly broad topic. But in essence I would say it is a good thing, though can fall prey to people craving power (same can be said about any government), becoming pseudo-socialism. But because socialism can be applied to various settings, small or large, it is significantly easier to implement properly. In which case we can see specific examples of where it has benefited societies.
In each case, what would make each of these types of government work, is an equally educated and equally treated society. One could say a more scientific approach as well. (I’ve always mentally teased a government with the base following the Scientific Method.) I have heard the argument “what about variance in culture?” and what not. But this is a false cry, simply to keep the status-quo. True equality wouldn’t hinder variance, it would allow it to thrive.
Which leads me to a Global Government. In some facets, we are already global. Economy and communication. A Global Government is inevitable. My optimistic side believes it is very plausible that such a government will eventually be one of the greatest steps in human (or post-human) history. True equality, an abundance of resources (mining asteroids, planets, a Dyson Sphere, etc), people basically doing whatever they want to do, elimination of money, etc. But my realist side knows that we’ve got a LONG way to go to get there. Thousands.. if not closer to a million years. Though I would guess with the advent of immortality, sentient AI, utility fogs, and other predicted future technologies, our societies’ mindsets will change drastically in short periods of times.. albeit not without perhaps extreme struggle.