Modern people love zombies because they illustrate a fundamental truth of a capitalist society - everyone is out to get you! More then that, everyone in the society is looking to fill their needs and their needs alone. Not that different from a zombie in a mob, since each individual zombie is trying to satisfy its hunger, and in no way is working in a group.
The end result works out in both cases to be something like an overwhelming force. Even though no single individual unit withing the group is actually working towards a common goal, the goals each individual within the group has set are similar enough that in the end the group can accomplish things that no one unit, or even small groups of organized individuals ever could.