Language as Social Signal:

I agree with what Sasha and Eugene have said about the descriptivist view of language, but I think language serves an instrumental goal that has yet to be explicitly described. By speaking (or at least attempting to do so) proper English, I not only potentially impress the elites with my intelligence, I send a signal to the population broadly that I am the type of person who knows and conforms with social norms. This signal labels me as a probable "cooperator" rather than "defector" in human interactions, and thus a good bet to treat them in a trustworthy way in a variety of social or business interactions that might arise. Someone who speaks improper English, much like someone who sports an eyebrow ring, signals a disinclination to comply with customary social norms, and marks themselves as a bad candidate for trust.