I've seen the argument that grammar should not be taught because it doesn't improve one's writing to study grammar. I say this is idiotic, because it assumes that the purpose of grammar is to improve writing. Grammar is interesting in its own right, whether or not it has any practical use in prose writing or not. There is a joy in paying attention to the syntax of things, despite Cummings. A good writer should be interested in language irrespective of the usefulness of this knowledge. At the very least, a knowledge of grammar will prevent one from making false & idiotic statements about grammar.
Also, I am impatient with people who profess interest in language, but disdain linguistics, either not knowing that it exists or dismissing it, thinking their folk beliefs about language superior to actual scientific, intellectually rigorous study of it.