Hummm. Interesting quote. I can see this, though. A fable is a story that typically teaches a moral or lesson. An allegory is a story in which the characters stand for themselves and something beyond themselves. LOF can be both, since the story is that of the evil or dark side of humanity. Each of the characters or groups of characters stand for themselves and an aspect of humanity. Ralph is the voice of reason. Simon is innocence. Piggy is knowledge. Jack is violence. The other boys are collectively survival, since they waffle back and forth between Jack and Ralph depending on who has the most clout. The longer the boys stay on the island, they first lose innocence (Simon is murdered) then they forsake knowledge (Piggy is murdered) and finally they stop listening to reason (Ralph). Reason would've been murdered if it hadn't been for the sudden rescue of Ralph on the beach by the Navy officers.
So, the lesson or moral here is beware, Mankind! How quickly does civilization disappear without innocence, knowledge and reason.