So you're defending capitalism based on imaginary capitalism in a utopian bubble, but you started out by trashing communism based on real-world performance.
That's weaksauce.
Same as any Communist apologist. They talk about how "that wasn't real communism, man" and bring up poverty and social injustice in the USA and historical anecdotes where people were treated badly in not-ideal-capitalist societies. Both extremes are utopian because nobody has ever gotten them to work as they supposedly should and they are both rather black and white and rely on a lot of theoretical assumptions being true to believe in their promises.
(I made some of the important parts bold.)
So if both extremes are Utopian, rely on a lot of theoretical assumptions and don't work as they are supposed to, then why did you say this following quote:
Of course utopian societies don't have things like corruption or ineffective institutions. Presumably some vaguely defined system of checks and balances with complete transparency in government would keep the ultra wealthy from having too much unethical influence in the government. With a minimal government having its hands tied in many matters it shouldn't be too corruptible.
(Once again, I made some of the important parts bold.)
Montague, if you want to be better than any Communist apologist, then don't fall into the same traps and fallacious arguments that they do. Let's keep the focus away from Utopian societies of either type, and focus on the reality of both systems, which is that pure communism and pure capitalism both are crappy systems of government.
Modern communism is simply an excuse for a totalitarianism government to seize and control businesses and industries. If any of these modern communistic societies actually followed Marx's teachings, the government would eventually give up its power to a collection of peaceful communes. Instead the governments tried to remain in power, even against the people's wishes.
Pure, or laissez-faire capitalism is a terrible form of an economic system because money speaks, and more money speaks loudly. Many politicians need money to run their campaigns for reelection, and not all of them are above taking bribes. And so businesses and the wealthy bribe the politicians to produce and support laws in their favour, laws that allow these businesses and people to earn more money, without concern about other people or the environment, because these people and businesses will never see the harm they've caused, or they simply won't care.