On Zootopia and the problem with using species as a metaphor for race or ethnicity

I thought Zootopia was fun, but I hated its metaphor, something that's bugged me at least since Spiegelman's Maus. A human race is an artificial concept, a tribe allows outsiders to join and insiders to leave, but a species is an immutable aspect of identity. The fox and rabbit of Zootopia can be friends, unlike the cats and mice of Maus who are genetically driven to be enemies, but they