Language is the toolkit of thought. If one uses the tools sloppily he will think sloppily. If one pays attention to his language tools he will make fewer errors in reasoning.
Tell that to the schools who are putting out push button brain dead students year after year.
The public schools don’t teach such useless things as grammar and spelling any more. My wife is a public school teacher but she teaches SPec-Ed kids and is ignored by Administration so she gets to teach such things to the ones who are capable of it.Some of her LD first graders at the end of the school year read, write and speak better than do mainstream kids in 2nd and 3rd grades .