This has been explored in linguistics. People do have an innate sense of grammar. However, language use changes over time, of course, and it's absurd to try to prevent that. Here's a good example -- as you said above, "People just know how to speak right." Of course, many English teachers would love to tell you that you're supposed to say "speak correctly" -- but why? It's a widely understood use of the word "right" and most people wouldn't think anything of it. Having standards about written language are necessary and helpful, but arbitrarily dictating the use of words based on their history is not necessary or helpful.