The zombie apocalypse scenario can certainly be a metaphor for racist anxiety, and there is no doubt they often take it that way. I think it is more universal than that, though, always serving as a metaphor for the specific prejudices and anxieties of the viewer or reader. To me, for example, the mindless brain eating hordes are a powerful metaphor for southern fundamentalists. For other readers and viewers, with different anxieties and fears, the metaphor represents a different threat. The zombie is always filtered through the perceptions of the viewer and becomes the feared “other,” whatever form that may take in the real universe.