>>81651691The idea, I think, was originally to make it more of a medieval allegory. The rats are cruel and vicious because they are rats, representing what we fear and hate about ourselves that we've put into "rat".
It doesn't quite work for a modern audience because we're (mostly) raised on, "You decide who you are." instead of the old, "Truth will out." ideas. Which isn't a bad thing, but is the source of that "Wait why are all the rats evil?" problem.
The fact that the author knew about this and sorta doubled down on it in Outcast and Taggerung was just a bizarre choice, but the series itself is worth reading for the early chapters.
Most strangely at all, the one species that escapes its mythological role are the 'dragons' of the setting and a mouse's greatest enemy: the cats, as you have an absolutely vicious cat and a kind, helpful cat in the same story.