Control and related themes of power and exploitation are basic to the voodoo zombie films. "They work faithfully and are not worried about long hours," says zombie master Legendre of his creatures in White Zombie, in justification of the capitalist organisation represent by the metropolis-like machinery of the mill.
Zombies of the Haitian Voodoo variety represent a loss of cognition/consciousness and also a loss of free will. What is it except these things, after all, that separates us from animals.
By "controlling" another person and eliminating that persons ability to make choices, let alone engage in conscious thought, the "controller" has reduced that person to the level of an animal and has robbed him of his humanity.
A distinct parallel might be drawn here between occidental cultures that have promoted the use of slavery and zombie films. To fear zombification, then, is to fear exploitation.