@glitterbag,
However this thread strikes you, gtb, the argument is not "silly".
Everything the contra-prescriptivist says is banal. It is well known that there are different ways of using language depending upon location, class, habit, pronunciation, accent, spelling and even different meanings to the same word.
A standard usage, as you imply, provides a unity. The land mass now known as the USA had many languages, as I gave an example of, not very long ago. Now there is a semblance of a unified standard which is a symbol of a unified political entity.
JTT is well known for drawing attention to the damage the US causes to the world and perhaps thinks that returning the area to what it used to be in terms of language use will eliminate the power. Which it would if there was a few dozen or more localised tribes and no prescriptivist base line.
The argument is not silly. It is silly to assert that it is.