GT,

There is a difference between regional or ethnic variations in a language and incompetence in the handling of its basic rules.

Go back several hundred years into works of English literature, from the plays of Ben Jonson to the novels of Walter Scott and you'll find ample depictions of dictions that deviate from the "standard" King's English, from the Cockneys in Bartholomew Fair to the lowland Scots in Old Mortality. What is noticeable about those dictions is that while they use alternative vocabularies or idioms, they are built on top of the standard English, not below it. There is a basic mastery of the rules of the language. Deviant characters and dictions are often depicted highly sympathetically, because they are lending color to the author's efforts, but where fun is poked at "low" characters it's usually, and rightly, when they mangle basic grammar. It's not difference that is being ridiculed but ignorance, or rather sheer stupidity.

That's why I disagree with the conclusions Robert McCrum reached in that PBS series.

It is not enough that "we all understand perfectly what is meant." If that were the case, we should perhaps allow children to drive cars across fields as long as they get to school on time.