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It is quite interesting to see the good old 'stabbed-in-the-back' myth over and over re-hashed. It was used by certain circles in Germany and Austria after the First World War went to Great Britain, France and the USA. even after World War 2 some die-hards thought the German Wehrmacht could have won if only home front politicians [that is, the Führer] would have listened to them.
As you point out, Mr Greenwald, American soldiers having been in Vietnam and civilians who never have been [probably even stronger than the soldiers] come out complaining about politicians and peacenicks. Part of this surely is political revanchism, but my guess is that soldiers need to believe in this myth to see their fighting as brave and meaningful.
Now, since in a war usually one side wins and the other loses, there will always be complainers, always be people talking about how brave and efficient the soldiers were; were it just not be for the back-stabbers.
Thought through in all its consequences it means
a) no war is ever lost by the military,
b) unless the fighting is over for a very long time it can never be decided when a war is lost or won, hence when to get out.
This state of mind is very consistent with the way wars usually start, be people out of words, out of thinking, out of creative ideas. In short, by people with a mindset similar to a 3-year old.