No one said it was a good thing. The question, which you yourself quote, was "will the downgrade of their debt status make dollars more or less desirable." Balki was explaining that it could make it more desirable for some. The US is opposed to it because it rocks faith in the US economy and could lead to government loans costing more money. That "more money" goes somewhere, and for them (those who get the "more money") it is desirable to own that US debt (which is in US dollars).
A more desirable pound, an increase in exports ..
Deny it all you want, the truth will surface.
Ok, I see, thanks for explaining it.