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.
It is said that power corrupts, but actually it's more true that power attracts the corruptible. The sane are usually attracted by other things than power.