Those who claim it has already arrived almost have it right, but not quite.

A zombie is someone who appears to have no inner mental life to you, but appears merely as a predictable pattern of destructive predation, based on a fixed programmed purpose. Unlike vampires who represent an alien but clearly live (if unpredictable and super-) intelligence that has an inner life and can adapt purpose to situation. You cannot reason with a zombie, but you can with a vampire ("if you let me live, I'll lead you to ten others you can drain.")

So a serious answer would be: if you genuinely believe in an ideological us/them distinction of some sort, the zombie apocalypse is already here _for you_. I call such zombies subjective zombies. To see zombies in others is to be a zombie yourself to "them."

This is because you cannot see or comprehend a zombie's inner mental life. Because it is in your Jungian shadow. But you _can_ see the predictable parts of their psyche, which makes them appear as automatons to you. And vice versa. Your predictable, shadow behaviors, mostly invisible to you, are visible and predictable to "them" and are the reason they are able to dehumanize _you_ into a zombie.

See this Q&A for examples: What is the most powerful "us vs. them" distinction in your life?

So a zombie world is a self-fulfilling prophecy.

So long as you relate to others only through their predictable behaviors, you can maintain a consistent zombie world view. If you allow them to surprise you, you might suddenly see them as non-zombies, and simultaneously see a zombiefied side of yourself.

In this extended and strained metaphor, vampires are fully realized beings, unpredictable to all, and free to be.

American politics involves Red/Blue zombies.