So Stross is describing his idea for an "ACME General-Purpose Space Opera Universe™" (lol) and notes that "faster than light travel would appear to be a necessary precondition to writing wide-screen space opera." He then repeats the conventional wisdom about FTL travel.
But if you permit violations of special relativity, you're also implicitly permitting global causality violation — time travel. (Go read a physics textbook if you're not sure why.)
This is the well known "Pick any two, special relativity, FTL, or causality" saying, and I've seen it referred to in other places recently. While true in general, it ignores the recent theories of physicist Miguel Alcubierre which allow for FTL travel without violating causality. As John G. Cramer explained in an old article for Analog,
The possibilities for FTL travel or communication implicit in the Alcubierre drive raise the possibility of causality violations and "timelike loops", i.e., back-in-time communication and time travel. Alcubierre points out that his metric contains no such closed causal loops, and so is free of their paradoxes. However, he speculates that it would probably be possible to construct a metric similar to the one he presented which would contain such loops. [emphasis added]
So while Alcubierre's drive is highly speculative it nevertheless shows that it is theoretically possible to have FTL travel without violating causality.
The second boner Stross pulls is in regard to the economics of his proposed space opera setting. While he gives the cliché of the space pirate an amusingly original twist it's still based on the mistaken assumption that capitalism can just be scaled up to interstellar distances. This is an idea author and game designer Greg Costikyan challenged in his 1982 essay "The 11 Billion Dollar Bottle of Wine," and in his non-fiction book Space Travel even arch-capitalist Ben Bova admits that interstellar trade in materials "seems doubtful."
Interstellar trade would most likely be in intangibles -- poetry, literature, art, philosophy. (pg. 214)
In other words, the scientific advances necessary to bridge interstellar distances will also be accompanied by economic advances.
Stross restates the truism that most space opera is just terrestrial imperialism projected into space. As his post shows, any attempt at making it realistic is going to come into conflict with the fundamentally unrealistic basis of the genre.