For those who don't know, I try to be very precise with my grammar. I also try to encourage this preciseness those people with whom I am closely acquainted. You may ask yourself why I do so. You may ask why you might do so yourself, not knowing fully why. Language is a marker of class, those who speak in the currently acceptable dialects are given more prestige than those who do not.
I have been reading about the effects of prestige language, and language imperialism. This happens all over the globe. Those who are dominant in a culture tend to control what is considered "correct" language. Whether the difference between two languages (Irish versus English), or between dialects (African American Vernacular English versus Standard English), or even accents within the same dialect, there are usually power struggles between those who speak the prestige language, and those who do not.
I have often seen acquaintances make fun of grammatical errors, as if having correct grammar somehow makes them superior to those who do not. While it's true that mastering some of the finer points of English grammar can make one feel triumphant (eg archaic word forms such as "whom"), it does not actually demonstrate a greater intelligence level. Rather, one's ability to speak prestige English seems largely to indicate what kind of family one was born into (likely a middle or upper class family).
(I don't think I'll even go into English's spelling issues. I understand why and how spelling works in English simply because I think that etymology and historical linguistics is a fun hobby. But not everyone is as much of a nerd as I am.)
As such, I attempt to school those who cross my path on the workings of prestige English. It's my own quiet way of encouraging social mobility. My mother, as an Algebra teacher does the same. She will assign a word for her students to learn, in addition to their math studies because she feels the same as I do. That language keeps people from truly being socially mobile.
At the same time I do this, I mourn that I am contributing to the destruction of a dialect. As has been demonstrated (by actual linguists, rather than hobbyists such as myself), the loss of a dialect can cause the loss of knowledge encoded in that language. With the assumption that a dialect does not fit into the ideal of the prestige language, is often the assumption that those who speak it have nothing worthwhile to contribute to society. This is often false. However, it is often human nature to assume those who are different from one's self are inferior. As long as we hold this prejudice, we shall not be able to allow people to speak in a different way from ourselves.
The Last Speakers: The Quest to Save the World's Most Endangered Languages by K. David Harrison
Linguistic Imperialism by Robert Phillipson