I believe the zombie thing is simply a product of a lack of a common real enemy. WWII is long over so no Germans to hate, the Cold War is over so no Commies to hate, and now we the war on terror but it would be quite faux-pas (and down-right racist / ignorant) to hate all Arabs. So now we have Zombies. We buy or toys and play with them and know full-well that "black rifles" are combat rifles that have been designed to kill people but this is taboo and we don't talk about this. Read any of these blogs were Joe Smith has an awesome AR or whatever to fend off Zombie hordes, all they are really saying is they have a rifle that is capable of killing many people. Think about it, replace the word "zombie" with "person" and voila.
It all comes down to "de-humanization" a term psychologist and sociologists use when explaining the process a person goes through while preparing themselves to kill other people. If you don't see your enemy as another equal human being it is easier to destroy them. That is why wars has spawned so many terms; towel heads, gooks, japs, Jerrys, yanks, etc.