@avi I was obsessed with this series as a kid and read all 20 something of them. This was always my least favorite aspect of the series - it was pretty racist and prescriptive! There are two books in particular that attempt to address this - Taggerung, in which an otter is raised by 'vermin', and Outcast of Redwall, in which a ferret warlord prince is raised at the Abbey by a hedgehog. Neither resolve the issue of inherent evil in a satisfying way. :(
@pexl And I did feel the same way about other fantasy series I was reading at the time.
I guess it feels more egregious in Redwall, because the animals aren't just walking talking metaphors (like in Aesop's fables), or mindless drones (like orcs/goblins/demons in a million different series). They have their own personalities, and seem like they should have the free will to choose to be good or bad. But that's not how it works.