The idea of correct language is normal in the wider community. It is not fashionable in modern linguistics, which is the science of language - and therefore seeks only to observe and provide a description of language. Modern linguistics - rightly - disapproves of the prescriptive approach, which aims to tell people how to write (or speak) properly. (Until well into the twentieth century, most writing about language was essentially prescriptive.)
AWE (this guide) is not a contribution to the science of linguistics. It is not descriptive. It is not prescriptive either. Its purpose is to guide and advise people who consult it. It is aimed at a particular group, students at institutions of Higher Education in the UK, with the particular purpose of advising them how to write in a style appropriate to their studies - that is, in a way of which their teachers will approve. Its aim is not to say "this is right: write like this". The intention is to say "Academic English dislikes [or even "rejects"] such a usage: you are advised not to use it" or "Academic English prefers the structure XXXX to the structure YYYY." Some articles say XXXX is an error, or "a common spelling error" when there is space; but we intend that this will be seen as a statement of what we, as teachers and advisers, have observed among learners. We would like to call this pedagogic linguistics. Users should notice that AWE offers choices to adult writers - at the simplest level, you may of course ignore our advice altogether.
As teachers, we aim to caution students against repeating errors that their predecessors have often made. We also hope to provide some positive advice ("This is a good way of saying what you may mean") as well as negative advice ("You are advised not to do this"); but because all writers are individual, and all good writers are trying to say something new, positive advice is rarer in AWE. Some is given at Good academic writing.
Users of AWE are asked never to think of it as an authority which can be quoted in an academic argument. It only gives advice.
Every student knows, or will learn, that there are certain usages that teachers hate. Some are slang expressions which introduce misunderstandings; some are words used inaccurately or imprecisely; others are cases where the student writer's taste clashes violently with the teacher reader's. In the last of these, two observations may help. The first is that you should remember that the teacher is trying to shape the student for a professional life, and conformity with some standards is one of the prices that entrants to a profession should observe. The other is that in the unequal power game of University life, the teacher has more influence over the student than vice versa.