I agree.
Also, I know a story about a Fox, that had 4 kits. There was also this old women who lived close by her den with her son. The Fox stole him, and she asked this guy to keep an eye out for him. He managed to get her son out in the end. So there is another story where the Foxes are shown as sly.
But I still agree. Erin hunter needed some evil guys in her story, and Foxes and Badgers were chosen. However, Warrior cats sometimes go too far.