Imagine a society that subjects people to conditions that make them terribly unhappy then gives them the drugs to take away their unhappiness. Science fiction It is already happening to some extent in our own society. Instead of removing the conditions that make people depressed modern society gives them antidepressant drugs. In effect antidepressants are a means of modifying an individual's internal state in such a way as to enable him to tolerate social conditions that he would otherwise find intolerable.
Our society tends to regard as a sickness any mode of thought or behavior that is inconvenient for the system and this is plausible because when an individual doesn't fit into the system it causes pain to the individual as well as problems for the system. Thus the manipulation of an individual to adjust him to the system is seen as a cure for a sickness and therefore as good.