@gailcalled
By “social” I meant that some usage writers have decided that a certain usage is wrong, in opposition to how the usage is actually used. The prescription has nothing to do with grammar or history, it’s a way to enforce social norms: use language my way, or people will think you’re stupid. And sometimes those usage writers are influential enough that they can’t be ignored.
“Without prescriptiveness, wouldn’t we have a lot of sloppy, hard-to-understand and uninteresting prose?”
Not necessarily. Some of the best works of English literature were written during a time when there were no dictionaries or grammar books.
Grammar and usage are separate issues, but you explicitly grouped literally and hopefully under grammar. There’s no grammatical reason why figurative literally is wrong. It’s undergone a completely normal semantic shift that has also happened to really, actually, very. It’s been used since the 1760s by well-regarded writers, who presumably knew what they were doing. Any cases of confusion are very rare, if they exist at all. The fact that the peevers are able to point out when literally is “wrong” is evidence that there’s nothing confusing about it.
I sometimes feel that by looking at how the language is actually used instead of how someone thinks it should be used, I’m understood as saying “anything goes.” Like because I accept literally as meaning “figuratively”, I therefore would accept any random change I could think of, like say apple to mean banana. But that’s ridiculous. I do think that in determining what the rules of English are, we should examine the relevant evidence. That is, how do the writers and speakers of English actually use the language? If writers use a certain construction, and it’s generally understood, and it’s sufficiently long-lived, I don’t see how it can be ungrammatical. It could be unstylish or silly-sounding in some contexts, sure. But it’s clearly part of English.