Whatever Happened to Iago?

Whatever happened to the character that just was, with no explanation as to why he was? There are glimmers of him every once in a while. Heath Ledger’s Joker was in love with chaos, teasing us with one sad back story after another, never letting us know which, if any, were true. But on the whole, even the most flat of bad guys have a flashback explaining how it all went so horribly wrong.
Is it possible, with all of our therapy and practiced introspection, that we can no longer take a character at face value? As readers, are we too into the mechanics of a personality to enjoy or loathe a character? If they do evil acts, shouldn’t our first thought be that they are evil instead of questioning how overbearing their mother was? Can someone be violent without having had the horrible pants wetting incident in school? Can we believe a hyper calorie-counter that was never teased for being overweight? Are we so trained to look deeper that we look straight through the surface?
As a writer, how do you use your audience’s expectations for a character to the story’s advantage? There is a temptation to give an explanation for every act, tracing it back through Freudian layers of childhood trauma. The problem is you can go too deep with a villain and in effect water down the admiration for the hero. After all, how many times have you felt sorry for a killer in a story once you discover he’s lost his own loved ones? It’s a balancing act that must acknowledge the complexities of personality while at the same time guide the reader towards the intended perspective. Motive is one thing, empathy is another.
Nothing is ever black and white in life, nor should it be in a novel that wishes to reflect true experience. The problem is, I find we are able to relate more to a fictional character than real people. After all, Meryl Streep helped us understand the pressure and sacrifice her Miranda Priestly endured in The Devil Wears Prada, but we rarely give our own boss’s possible stress a thought before labeling them a jerk.