Being a language geek, I eventually found out that grammar textbooks were brainwashing me. They explain a theory, which is just a theory, as if that's the truth. They told me that dialects and slangs were bad languages, that the good language was what was in the grammarbooks. They sometimes taught theories that most scholars don't agree today, such as the three-way contrast of the Korean consonant system. Textbooks told me that there is a three way distinction based on how "strong" the consonant is. In reality, scholars haven't reached an agreement on what the distinction is based on. They know very well what those phonemes' allophones are. They just don't know if it's based on aspiration, or tone, or stiffness of the vocal cords, consonant length, etc. Imagine a science textbook that confidently says that earth is the center of the solar system. Then imagine a grammar texbook saying that it's "whom" not "who". They're equally ridiculous because they're explaining obsolete theories. They're terraforming people's minds with obsolete theories that only benefit the producer of that information.