All pure philosophy fails at the extremes.

Making idealistic arguments, to me, is either foolish or disingenuous. Ideologies are all wrong. Everything is a compromise. The only constant in society is change. If you're making an ideological argument you're either (a) imagining some universal absolute that only exists if your concept of a deity is correct, or more likely (b) projecting how you wish the world was onto how it actually is.

Capitalism, for example, is a general good. The aggregate of the decisions of a million individual actors IS a better market than one dictated from on high. But unlike someone else in this thread, I don't think the failures of capitalism can be explained away by a lack of perfect information. Even with perfect information, our individual actors will always have different motivations. There will always be those who cheat and defraud, for example. There will always be those who seek to monopolize. There will always be those who choose short term profits or convenience over long term costs that they will not be alive to have to pay. However much idealists can scream about how things will work out in the long run, they don't always.

Similarly "freedom" is not an absolute good. Freedom is only good if you want it. Not everyone does. Plenty prefer the security and predictability that can come in a well-directed totalitarian state.

People ARE different, and as such large heterogeneous nations can be unwieldy. But people do change, as do cultures and societies. Mostly that comes about through communication. Ideas are shared and the more useful ones win out over time. For 99.9% of human history the biggest barriers have been geography and distance. All of a sudden that is no longer the case and we're seeing a tremendous about of upheaval as a direct result. It will take generations for this to smooth out, but I suspect it will eventually, and the result will be far more homogeneity and far less Balkanization.