In his extended discussion with Mustapha Mond, John the Savage questions why there are five different castes, especially as the lower castes are forced to lead very restricted lives doing menial labor. Why not, he asks, since it is possible to do so, make everyone an Alpha-plus, in other words, of very high intelligence? Wouldn't society thrive if everyone were of the top potential?
Mond responds that the Cypress Experiment tried to do just that. This experiment put 22,000 Alphas on the island of Cypress by themselves with no other castes to help them. The experiment, as predicted, failed. The Alphas all wanted to do the top jobs that took the most intelligence and involved assuming the most responsibility. Nobody wanted to farm the land and nobody wanted to toil in the factories, so the land wasn't "properly worked" and "there were strikes in all the factories." Everyone spent their time plotting and planning to get—or keep—the top jobs. Alphas, having the capacity to think for themselves, also disobeyed laws and orders. Within six years, they were embroiled in a civil war that killed 19 of the 22,000 of them.
You need difference, Mond explains, because everyone can't be in charge. Society runs more smoothly when most of the people are born with mental limitations and then conditioned to be content with their restricted lives. As Mond puts it:
The optimum population ... is modeled on the iceberg-eight-ninths below the water line, one-ninth above.
He insists that the eights-ninth "below," who simply do routine work and don't have decision making power, are happier than the Alphas, because their lives flow along on a simple groove. Mond explains that their work is:
light, it's childishly simple. No strain on the mind or the muscles. Seven and a half hours of mild, unexhausting labour, and then the soma ration and games and unrestricted copulation and the feelies.
The World State has made stability and order its supreme values and is willing to dehumanize eight-ninths of the population to ensure this stability.
John the Savage is appalled that almost the entire population is denied access to life's highest and most humane values and endeavors: deeply loving relationships with close family and a romantic other, a religion that stretches people to behave in the most ethical, sacrificial, and giving way possible, even if it causes the individual pain; and the chance to read challenging literature, to create art, and to pursue real science.
John would define difference differently than Mond. To John, it is the freedom to think, feel, read, create, suffer, and choose your own path rather than be conditioned into robotically thinking and behaving like everyone else. Creative difference, to John, is what makes life worth living. Social stability is not worth the price the World State exacts, he thinks—and we as readers are encouraged to agree with him.
To Mond, however, having a safe, secure, and superficially happy life is more important than these highest of human values. He would, therefore, rather differentiate people into castes, even if this stunts most of them, than to tolerate the creative chaos and problems an intelligent society would produce.