Economist Style Guide double negative

SIR—At times just one sentence in The Economist can give us hours of enjoyment, such as “Yet German diplomats in Belgrade failed to persuade their government that it was wrong to think that the threat of international recognition of Croatia and Slovenia would itself deter Serbia.”
During my many years as a reader of your newspaper, I have distilled two lessons about the use of our language. Firstly, it is usually easier to write a double negative than it is to interpret it. Secondly, unless the description of an event which is considered to be not without consequence includes a double or higher-order negative, then it cannot be disproven that the writer has neglected to eliminate other interpretations of the event which are not satisfactory in light of other possibly not unrelated events which might not have occurred at all.
For these reasons, I have not neglected your timely reminder that I ought not to let my subscription lapse. It certainly cannot be said that I am an unhappy reader.
—WILLARD DUNNING