There is no set of standard grammatical rules for any language. There are current standards for existing dialects, and they change all the time. The strict and steadfast rules of a Londoner’s English are different from those of a Bostonian’s English or Californian’s English. And go back fifty years and those rules in all of those places were different still. Your prescriptivist nonsense is not based on material reality, and you are using it to justify nothing short of your racist prejudices