Yeah! Prescriptivist grammarians are annoying, controlling lot! But grammar itself —not rules but the study of how humans put morphemes together to form lexicon and syntax— is endlessly fascinating. Noam Chomsky created quite a stir with his ideas about a "universal grammar machine" biologically wired into all human brains. His hypotheses ultimately turned out not to be supported by evidence, at least so far and not looking good that the situation will change. But! The study of grammar itself is super interesting.

It's frustrating that the sort of grammarian you were describing usually doesn't know anything or much of anything about linguistic theories of grammar.

If they did, they'd probably be a lot more open-minded.

Here's to hope!