It has long frustrated me when people use "grammar" to cover usage, orthography, punctuation... I understand that better now! If people associate "grammar" with shameful mistakes, with arcane rules that push them down or let them push others down, then the confusion makes sense.

Thank you! This is the definition that most people have, and it just makes them hate language because they’ve been exposed to so much shaming.

My favorite analogy about it is to clothing. Language, like clothing, has functional aspects. However, there is also a social conformity element that is far more restrictive than the functional requirements, and adherence or deviance from those norms acts as signifiers of in- or out-group status.