"the reason communism and socialism don't work is that controlling decisions sensibly from the top-down is not feasible.
consequently, many decisions get made from the bottom-up. the ones that work tend to flourish. the decisions that don't work tend to end up doomed."
let me explain this.
in capitalist and mixed economies, many decisions get made from the bottom-up. governments are not the efficient mechanism for making many sorts of decision eg the price of pork belly futures.
and some decisions do get made from the top-down: things like printing and securing money, setting market regulations, running certain systems not governed by the profit motive (eg healthcare), correcting negative externalities (eg pollution).
there is a whole world between the twin poles of unregulated capitalism and a control system like communism. i think of this as the temperate zone, in which all sorts of economic life can flourish.
democracy is not capitalism or socialism. those are choices any democratic society can make for itself.
democracy is rule by a subset of the people (eg children tend to be excluded from the vote). representative democracy is rule by the people's representatives. in filtering popular will through representatives you can get a layer set of issues, such as the influence of money.
there is a legitimate question about the wisdom of the voting population and another one about corruption via representation.
the us constitution does not deal with these well in every circumstance. eg sometimes people vote for charlatans and sometimes the system seems to favour incumbency over innovation. these are common problems in every society. fortunately, in a democracy the feedback loop means you can always throw a party out. and some systems are run with only a veneer of democracy because, frankly, popular will doesn't mean economic insight - so the federal reserve operates somewhat independently of politics during the term of office of the members, and the same goes for judges.
dictators, monarchs and emperors have their own set of issues. study ancient rome, byzantium or the long-haired kings of merovingian francia (the rois fainéants) if you want to understand the difficulties eg of nepotism and inheritance. generally, they work less well than democracies over time as the feedback mechanisms tend not to function. every now and again, a benevolent sovereign does okay.
general principle: any system in which the ruler is not subject to law is a poor system for the governed.
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