People have always strongly believed, and taught, things about their own languages and languages in general. They're not all wrong necessarily. But linguistics over the last like 80 years has produced some models that have incredible predictive and explanatory power, and are incompatible with a view of an objective "correct" or "best" or "standard" form of a language.

There have certainly been efforts to draw arbitrary distinctions between groups based on speech for a very long time, probably going almost as far back as language itself.

What I was referring to was specifically an effort rooted in a desire to use rules of Latin grammar to restrict constructions in English. This was a big thing relatively recently (likely sometime in the past 100-300 years). It is this movement from which we get rules like "never end a sentence with a proposition" or "don't split infinitives" --- those sorts of things.