Why are Zombie movies so popular

A big part of what makes the zombie genre so much fun is that it puts us in a situation where we have to fight for survival against an enemy that's incredibly similar to ourselves. Often times the reason zombies make such appealing villains is this similarity. The key difference is that because the zombies are not "human" or even really alive we don't have to empathize with them at all. It makes no difference to us whether the zombie are subdued or simply destroyed. The hero's methods for overcoming the zombies never bring to question his or her principles; they must be defeated in any way possible.