As Mustapha Mond explains to John the Savage near the end of the novel, the ethical calculus he uses puts the highest value on security and happiness.
After the Nine Years' War, Mond states, people were weary of fighting and willing to give up their freedom to have peace and plenty. Therefore, to Mond and the other controllers, nothing is more important than ensuring a smoothly-running society in which people are superficially happy. Mond is willing to throw strong emotions, family, passionate love, real religion, real science, art, and literature under the bus to keep society stable and secure.
Mond states that after the Nine Years' War:
What’s the point of truth or beauty or knowledge when the anthrax bombs are popping all around you? That was when science first began to be controlled—after the Nine Years’ War. People were ready to have even their appetites controlled then. Anything for a quiet life. We’ve gone on controlling ever since. It hasn’t been very good for truth, of course. But it’s been very good for happiness. One can’t have something for nothing. Happiness has got to be paid for.
Mond believes the trade-offs have been worth it because he believes that safety and happiness are all important. John, on the other hand, is appalled, feeling that this new society has given up everything that makes human life worth living.
John asks the Controller why the society doesn't tell people about God, saying that such information might help people to live less "degraded" lives. This, John states, would build character and allow people to bear their troubles patiently. The Controller responds that there is no need for such patience because modern society can eradicate all need for unpleasantness and self-denial.
John assert the right to be unhappy; Mond says there is no need for unhappiness in a perfectly controlled society.