That’s the thing. Nobody is. Words were not handed down from god. Language changes continuously. Notice how we aren’t speaking proto-indo-european any more?
I'm trying to avoid this conversation :-) I think descriptivism/prescriptivism is probably off-topic in this thread.
Oh well -
Someone upthread implied that the purpose of a descriptivist dictionary is to help readers/hearers to understand unfamiliar words, not to guide writers/speakers in correct usage. Thing is, they're all descriptivist. There are opinionated guides like Fowler (and the subject of this article! /on-topic), but I don't know of an opinionated lexicon.