Well, actually what i mean by darkness as in showing Batman's dark psychological side more.
I have to say you have a me at a loss here. I'm trying to recall what movie you're refering to, because when I've watched the Dark Knight, the only struggle that I saw Batman going over was whether or not he should retire and get together with his childhood friend.
Now unless you're talking about his desire to kill or not to kill villians, that is more of a moral dilemma than a psychological one. A dilemma that I think is stupid to be honest. I mean say for instance yes, Batman keeps his moral high ground by not killing the Joker. Meanwhile the joker is racking up a body count every time he gets loose. Thanks Batman, you get to keep your clear conscience while the rest of Gotham City burns to the ground. Way to go!
Police officers have to take the life of criminals a lot of times while in the line of duty. Its an ugly part of the job, but sometimes it has to happen to insure the safety of others as well as your fellow officers.
Either way the movies hasn't touched the dark psychological parts of Batman's mind. Honestly from the Nolan movies stand point he hasn't been doing it long enough to develope that yet. I mean when the part of his mind that is Batman finally developes into a separate personality, then yes I'd say they've gone there. If he has moments where the part of him that is Bruce Wayne clashes with the part of him that is Batman, and they have a verbal arguement, then yes I'd say we've gone there.
But the Nolan films really haven't yet. Maybe in the future but not presently.