Writing at The Guardian, the estimable Stan Carey has presented a stout defense of the language people, especially children, use, including slang and regional dialect.
He attacks linguistic prejudice (which almost always rises from class prejudice) wedded to unsound pedagogy. He leaves no room for the anything-goes, all-is-permitted cry of the sticklers, who typically argue that if you relax one single stricture all English is lost.
You will want to read the whole article, but I can't resist quoting salient passages:
"Native speakers of English are generally at least bidialectal. We have the dialect we grew up using, with its idiosyncrasies of vocabulary, grammar and pronunciation, and we learn standard English at school and through media like books and radio. As with any social behaviour, we pick up linguistic norms and learn to code-switch according to context. Just as we may wear a T-shirt and slippers at home, but a suit and shoes at work, so we adjust our language to fit the situation.
"Standard English is a prestige dialect of huge social value. It's important that students learn it. But the common belief that nonstandard means substandard is not just false but damaging, because it fosters prejudice and hostility. Young people can be taught formal English, and understand its great cultural utility, without being led to believe there's something inferior or shameful about other varieties."
Here's the unsound pedagogy:
"Linguistic vetoes can be counterproductive pedagogically too. Sociolinguist Julia Snell argues that 'to learn and develop, children must participate actively in classroom discussion; they must think out loud, answer and ask questions'. When the focus is on the forms of speech instead of its content [emphasis added], she writes, 'children may simply remain silent in order to avoid the shame of speaking 'incorrectly', and miss the interactions crucial to learning'."
And the prejudice:
"People feel strongly about correctness in language, but this strength of feeling isn't always matched by knowledge and tolerance."
People will talk the way they talk, and if you try to repress young people's slang and dialect, their innate human cussedness will foster greater resistance. This is why schoolteachers' policing of language is so misguided: It produces either rebels or prigs. Or mumblers.
The grammar scolding one sees online is similarly misguided, because grammar scolds are not actually interested in correcting other people's language so much as they are determined to demonstrate their own superiority. They need other people's "poor grammar" to bolster their own identity and self-worth. This is how prejudice works generally; the hater is dependent on the hated.