Brave New World by Aldous Huxley essentially serves as a refutation of both utilitarianism and highly planned societies. The utilitarians argued that the goal of political ethics should be to achieve the "greatest good for the greatest number" and defined the greatest good as maximizing happiness. In Huxley's novel, we see that the happiness is achieved at the expense of the self-actualization of a minority of individuals who do not fit in or conform to social norms.
For Mond, truth can remove many of the comforting illusions that cause his society to function smoothly and effectively. This is not a point unique to him or to Huxley. Even in our normal social interactions, when we compliment a hostess on a dinner or a friend on a new haircut, often we say things that we do not believe to be true in order to make people feel better. Telling, for example, a date that we do not want to see him again because he is boring and has horrible table manners causes pain to no purpose.
Mond is making the same argument on a social level. Most of the people in his society are happy, something guaranteed by the way society is organized and by the use of mood-altering drugs. His point that telling them unpleasant truths would wreck a system that is generally beneficial is not entirely wrong. In fact, for example, the contemporary Chinese government would argue that this sort of authoritarian society which suppresses dissent for the sake of harmony functions well for their culture and has resulted in a society that has lifted itself from poverty in almost record time. One could argue that Mond poses a serious challenge to a western conception of freedom as an ideal, a conception that is far from universally or globally held.