Haha, no, it's not a pejorative. It's literally one of two schools of thought: descriptivism vs. prescriptivism. What you're describing is prescriptivism.
I didn't suggest it was pejorative, and I know what it is. There are not two school of thought, that's a false dichotomy. That is like saying "there are two schools of thought, catholic and protestant". You can want to prevent the decline of language without insisting on trying to bring back already lost definitions like a prescriptivist.