The Zombie has many links to what Gustav LeBon called "The Crowd", his 18th Century book studying and describing the actions and reasoning behind rioters, the angry mob, etc. These can also help expose the reasoning why people are so willing to release the pressures of decision making and control of their own lives to join a cult, religion, army, or gang. It's why stable and unassuming people joined the Manson Family, the Branch Davidians or the 3rd Reich; why these people were able to be convinced into doing inhuman things as a crowd or group, which subsequently releases the individual of personal responsibility. It's not one person dragging the handicapped, Jews, gypsys and homosexuals into gas-chambers, it was the group. It wasn't one person killing and raping children and then poisoning themselves, it was the group. The zombie is the representation of the unassuming person, who is capable of doing terrible things when they are immersed in a group of like-minded people who also have little willpower. We assume those people must be dead inside to simply go with flow of the crowd and follow the words and urging of one captivating person like a prophet or a dictator. In the case of the zombie, we actually make them dead so we can empathize with their horrendous actions, with the living we don't.