We throw around disorder names like obsessive-compulsive and conduct as if they are singular entities. Many people, upon seeing victims of these illnesses, tell themselves that they are glad to not have these disorders. I argue that such behaviors are inherent in all of us. Everyone, at some point, has experienced a moment of "enhanced behavior" . . . some alternate state when their actions were just a tad off, but this change allowed them to do remarkable or abnormal things.
Perhaps the next step in psychology or therapy is not to suppress these tendencies, but rather to have the ability to bring them on at will. Such an endeavor would allow us to change our moods, work habit, levels of aggression, etc., almost instantaneously. Certain conditions warrant such change. I think that these changes should be self-driven and cognitive, not medical or biologically-started. With this change, one would learn supreme self-control; indeed, he or she who masters such a technique would almost have to rank on Maslow's hierarchy as self-actualized.
Almost as important (likely just as important) as creating this change would be its ending. To be able to switch on an aggressive mood and be able to turn it off would be a disaster and would most likely lead to immediate outside action. I would hope that having the mental dexterity to start such a change would automatically allow the person control over the opposite action.
As I mentioned earlier, these "moods" are present in us at all times. The reason that they don't show in our actions is because another "mood" is balancing it out, just as one drug can balance out the effects of another. Similarly with that analogy, there are still side-effects to the process. Anxiety, lack of energy, and depression are three consequences that come quickly to mind.
I think that insanity is a person or brain that finds such a state to be preferable to the current situation. Sure, there are some disorders that don't necessarily have a positive function, but I don't believe these to be singular issues. Instead, they are simply the progression of a more "useful" mood. While a situation has pushed a person from the "normal" part of the behavioral spectrum, past any useful state and into insanity, such people do not possess the skill to bring themselves back.