@pexl I was reading it when I was in my early to mid-teens, so that aspect ran thin very quickly. I really enjoyed "Martin the Warrior" because it was a ripping yarn, but the black and white morality combined with "all [x] are born evil" turned me off when I tried reading other books. I knew it was for a younger audience and didn't expect deep philosophical discussions, but it definitely made things less fun.
@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.