Since you're the writer of the original article, why did you choose to use the British Nationalist Party remark (which according to the article was an aside) as the main title here instead of the real title of the article ? ("Charles Stross slams 'tainted' US politics'")
It seems that the latter was the more descriptive title.
As for Charles' criticisms of US policy, the quote you make:
"There is a cancer in the collective American soul — a mercy deficit that has in recent years grown as alarmingly as the budget deficit. Nor is it as simple as a left/right thing: no political party has a monopoly on merciless behaviour. Rather, a creeping draconian absolutism has cast its penumbra across the entire arena of public discourse, tainting every debate, poisoning and hardening attitudes across the board."
Like all generalizations, it isn't perfect, it paints with too broad a brush. But the essence of the remark remains unanswered by your writing. I know plenty of great Americans as well, but on the whole they'd find themselves in agreement with Charles Stross more than they do with you.
By denying a problem exists you make it worse.
If Americans think Texas has a appalling record on capital punishment (your words) then they should do something about it.
"which paint all participants in the political process, even the self-sacrificing ones with everyone’s interests at heart, as cynical, cold-hearted and without mercy." Is a far cry from what was actually said.
I interpret the 'no political party has a monopoly' to mean: You can't hide behind saying it's the others, there is plenty in your own ranks. It does not address any individuals.
Anyway, I read the whole Charles Stross posting, not just your 'excerpt' and came away with the idea that he's got a lot more balance than what you suggest.