Appeal to authority is acceptable in general academic practice but it is not logically valid as such. The datum that X is an authority on subject S does not support or refute a proposition of fact about subject S, let alone about some other subject, regardless of WHO wants to be cowed by it. It is, logically, irrelevant. People accept it because it seems to them that if an "expert" or "authority" says something, it has a "high probability of being true" or at least accepted -- so it seems to be a safe bet.

Anyone who has been around the block a few times knows that can be a very risky assumption, and I speak as an authority on human experience!! :>)

A