I'm still trying to figure out how the mouse community is viewed as the 'good' race of rodents when they send LITTLE BOYS down dark holes to be eaten by rats if they...well, are different. What the heck is this doing in a kid's movie?
I don't think they are. They're viewed as a flawed society that's only hurting itself by refusing to accept anything new or different. Isn't that a major theme in both the movie and the book?
Basically the difference is that the mice are a highly oppressive, stale society that refuses to accept anyone different, while the rats are an evil, cynical society. From a certain point of view, the rats could even be considered "less evil" because they, at least, are honest.