Just a note of caution but i'm about to get weird up in this piece...
Zombies themselves certainly aren't very attractive or appealing in the sense of fictional monsters. They don't offer a lot in terms of drawing the audience in, causing us to hate them like the more memorable nasty bad-guys like vampires, aliens, or murderous mutant cannibals. Their intimidation more rooted in their sheer numbers than anything individual. They simply lumber (or run - depending on if the storyteller really wants to paint a bleak picture) around and attack mindlessly, bent only on one thing void of reason or logic. They are not psychotic killers. They are more like animals. We probably would see them as we would a bear or wolf; very dangerous but avoidable. It seems that presently what is so frightening about them is how we identify with them. We're led to believe that they were once regular people with families, jobs, dreams, fears, etc; just like all the rest of us but now they are something else entirely; debased and simply driven by one thing - the satisfaction of their hunger. They act solely on impulse and instinct derived from the one thing they want. The object of their hunger has been many things - brains, the advancement of their virus, something more sinister - but it is sure that they are willing to pursue this hunger at all costs, even to their own detriment.
This is where i think the most terrifying part of the story is found. We realize, if we are truly honest with ourselves, that this sort of mindset exists in us all. In recent history, society has fostered a destructive psychology of self focus. We are taught that the most important entity is one's self. One's happiness is the ultimate goal. Shakespeare famously penned the phrase "to thine own self be true" many generations ago and our society has broadly personified this philosophy. In the first part of last century, an infamous cult leader, Aleister Crowley, preached his message of "Do as thou wilt". He spread his message of self-gratification at any cost, even human life, as long as one's own appetites were satisfied. This doctrine has gradually infiltrated the common psyche over the years reaching the masses through music and entertainment. Most people can recognize the shrinking shift in the common worldview over the past century. Though we are connected globally and generally more educated about other ways of life than ever before, we are also more confined and isolated in our own little spheres, all the while sharpening our sense of self. Technology, though a blessing in many ways, has also caused us to be self-absorbed; worrying mostly about our own interests and dismissing anyone else's. This is the world we live in. You can go anywhere and see thousands of people not looking at anyone else but simply hypnotized in their own world, ministering to their own desires, staring at the window into their own soul - their phones. What is the end-game for this type of society? If art imitates life, how would art draw a picture of the apex of this collective existence, given free reign over the souls and minds of men?
i believe it's in the zombie genre that we see the expression of subconscious discomfort with the idea of exalting self above all others. What are zombies if not first selfish? They are the culmination of the unbridled self - willing to kill to get what they want. These movies and books are metaphor for the imagined future state of man's existence if allowed to let self reign unharnessed. We already see glimpses of this in parts of the world where order and justice are deteriorating. When people see that there is no repercussion for pursuing self-gratification they "throw off restraint" and steal, rape, and\or murder to get what they want. The allegory of a world lost to wandering corrupted souls searching for self-pleasure alone should not be overlooked.
Now, the spiritual connotations of all of this:
The story usually originates with a disease or sickness that infect people causing them to "turn". In many of the stories that disease is inherent, meaning it doesn't need to be transmitted it simply is lying dormant until activated. i feel this is where we all are. We all have the sickness of self. We have elevated our own ambition and pleasure above our fellow man and ultimately above God. Some of us are more acutely aware of this weakness and attempt to overcome it by suppressing self which creates a house of cards waiting to collapse into the next pride induced failure. We need an out. We need something bigger than ourselves to rescue us from this ever-deepening cycle. We can never be free of self. Our own ego and selfishness are ever present. We can have a paradigm shift in our perspective. We can be given a greater view. A view where we see others as greater. A vision where we are awakened to the beauty of love and sacrifice. We can only be awakened from this trance of self-sufficiency by looking at the face of selflessness; at the face of Jesus. There is no greater love than to lay down one's own life. Sin is the disease and self is the sickness but the love for God and for others is the cure. You also see this redemption theme play out in these stories. It is peculiar that in our broken expression of soul - art - we understand where the world has gone wrong and we also understand how to overcome it.
Though most of these movies and books are garbage that i wouldn't recommend to anyone there is a picture being painted with a meaningful purpose. The culmination of pride is complete corruption where all people are consumed with their own self-gratification. The lesson to be learned is that without sacrifice for other derived from the love of God and others there is no fulfillment, only destruction.