Horrible grammar is fine in dialogue if it suits the character who is speaking: but iffy grammar anywhere else is a sure way to get rejected.
Grammar isn't elitist; it isn't a set of rules designed to exclude certain people: it's part of a code (the other parts including punctuation, spelling, logic and rhetoric) which has evolved in order to ensure clear and effective communication. You can object to it all you want, but if you get it wrong your meaning won't be clear. And as writers, isn't communication our aim? Communication of ideas, stories, themes: if we don't communicate effectively, we're stuffed. So, if we don't bother with grammar (or logic, punctuation, spelling and the rest), then we're failing before we begin.