True brilliance has a well-known positive correlation with decency, much of the time-a fact the rest of us rely on, more than we ever know. The real world doesn't roil with as many crazed artists, psychotic generals, dyspeptic writers, maniacal statesmen, insatiable tycoons, or mad scientists as you see in dramas.
Still, the exceptions give genius its public image as a mixed blessing-vivid, dramatic, somewhat crazy, and more than a little dangerous. It helps promote the romantic notion, popular among borderline types, that you must be outrageous to be gifted. Insufferable to be remembered. Arrogant to be taken seriously.