I think you're searching for reasons to disagree based on semantics and technicalities and evading the very cogent points made by the author. While there is room for disagreement about some of the nuances of what is meant by "Capitalism" or "democracy", do you think that there is really any comprehension problem w.r.t Stross' use of those terms? It seemed perfectly clear to me. His usage is quite conventional.
What about the quoted passage do you actually think is ambiguous?
It always struck me that socialism is the economic system that in theory appears to be closest/compatible with democracy. Then again, I think what has actually become obvious is that mixed economies are what seem to work, to which I'd add not just having rules, but changing them often enough to prevent gaming of the system. So maybe in a sense messy is good not just because the real-world requires messy solutions, but because you got to keep people on their toes. Let's face it, laissez-faire or pure socialism, the weak point in either case is people subverting the system.
It's tough to respond to statements like this as written. 'Capitalism', 'democracy' and 'work well' are not precise terms, and the statement can be either true or false depending on the shade of meaning.