I read on the Duolingo blog that there's no such thing as right and wrong English. The owl claims that language is constantly evolving. For instance, saying 'You're good.' Is acceptable English. Good is an adjective. Well the adverb. You telling me that I am good is like having a cockroach grade my differential equations exam and giving me a good grade. The cockroach might say I did well on the exam. The cockroach would not be able to say whether or not I am good. Particularly with regard to differential equations.
If there's no such thing as right and wrong English, how could high school English teachers grade exams?
The loudest, most offensive English firsters tend to be least able to speak English. I am not an English firster. For instance, there's no reason a commercial driver must speak English. In many nations, multiple languages are used, and a police officer would be expected to speak several if not all of those languages. A multi lingual police officer might not be fluent, or even willing to communicate in the language of a commercial motorist the police officer had detained. That does mean that the officer must disrespect the motorist.
Police officers, unlike almost every other profession, are seen as either all good or bad. You wave a blue American flag or you don't. There are good police officers and bad, just as there are good and bad doctors. The idea that an American motorist must communicate in English speaks more to many police officers being stupid crackers that cannot learn a second language. Or at least use a translator.