I think this Joker was so freaking smart and cunning, that he planned everything, even how to mess with peoples perception of him, like the scars, he knew they (cops, Batman, Dent) would try to see them a mark of a tragic event, thus manipulating them into other events in the future until Batman figures it out that he's just messing with everyone, and it's useless to confront him by the psychological side, being that he always has the advantage due to his none explainable behavior.
I know parts of the movie may be seen as real emotion outbursts by the Joker, but, maybe it's just how he thinks the present attitude he's taking would react, being that he acts always, sometimes as childhood abused, love tragedy, or just someone who doesn't want to be alone, but this are just temporary mediums to chaos, meaningless masks, I think we would've seen a very different Joker if there were a sequel with Heath, by different I mean expanded, with a really broad spectrum of personalities. But that's just me