In Huxley's "Brave New World," Mustapha Mond is an extremely powerful man—he is the Controller of the world. He is, like many such characters in dystopian novels, well aware of the inequity in what he does, but has long ago rejected any such worries in carrying out what he views as the greater good of society.
Freedom, individuality and human will are things that the state, under Mond, cannot abide. They are in conflict with what Mond views as happiness, which is stability, lack of conflict-causing emotions, and the management of any "glitches" in the system—people who upset the order. Mond sees this type of restraint—not allowing any individual personal freedom, only relative freedom, as defined by the state—as constituting the happiness of greater society.
The character of John, the powerful yet intelligent primitive, is the antithesis of what Mond wants in his world. John represents the unstoppable forces of human nature, which societies such as Mond's can never truly contain.