Arguments of prescriptivism vs. descriptivism in linguistics have been going on for many years. And certainly the pure prescriptive approach is untenable. To argue that today’s version of RSE (Received Standard English) is simply “correct”, and any deviation from it is “incorrect”, is absurd. Same goes for any other language. For example, the French police their language closely, even using a nearly 400-year-old quasi-governmental group called L’Academie Francaise to guard the “purity” of French. Yet French would not even exist if Latin had not been “corrupted” to a degree that would have horrified the prescriptivists of 2,000 years ago (and I’m sure there were some even then).
On the other hand, I think pure “anything goes” descriptivism misses an important point. I don’t see anything wrong with grammatical rules evolving, new words entering the language, or the meaning of words shifting over time. What does bother me, though, is when two words that once had at least subtly different meanings converge in meaning and become pure synonyms, but no other words emerge to convey the distinction. This leaves the language both less enriched with ways to convey meaning, and more needlessly difficult for children and non-native speakers to learn. (They may only need to learn one of the two words to make themselves understood, but they’ll have to learn both to understand others.)
And it ensures a confusing transition period during which it is likely that older speakers will be confused, or at least annoyed, without any corresponding compensation in terms of enriching the language. Therefore I do think it’s warranted to at least attempt to be prescriptivist in a narrow sense when you see this beginning to happen. If there’s an overwhelming tide, you might as well not even try: at a certain point you’re just a “get off my lawn” crank tilting at windmills. But I think these things can and should be nipped in the bud if enough people jump on them early enough. The naggers (or “S&G Nazis”) may still annoy a lot of people, but they are doing good work if they specifically target the kinds of words I’m referring to, and avoid being needlessly prescriptivist just for its own sake.
What’s an example of this, you ask? Well, there are two that come to mind at the moment, although over time I have noticed scores of examples at the very least. But these two came up quite recently in different podcasts I was listening to regarding TV shows. The people talking otherwise came across as educated and well spoken.
(1) “Murder” as a synonym for the berb “kill” or the noun “homicide”. The context: Character A killed Character B in what was quite clearly self defense (I’ve also read or heard it in contexts where you might, at the very most, be able to charge someone with something like second degree manslaughter or negligent homicide, but certainly not any kind of murder).
(2) In a similar vein, “rob” as a synonym for “steal” or “burglarize”. If someone is unarmed and sneaks into an empty house and takes the jewelry, it’s not a robbery!
Other examples are welcome. And feel free to push back if you think a broader descriptivist stance is warranted.