Now that I've seen the entire Nolan arc, I would state that he's used Batman very effectively as a means to investigate, and in effect parody, the power that the nation-state uses in things like fighting terrorism.
A city in crisis essentially appoints one man to save them, to fight for them. That can work only because Bruce Wayne is an immortal icon, with incorruptible values, and exists with a power that isn't granted by his actual personal power directly but by assuming the guise of a theatrical legend. In real life, we have no such icons.
We have only men and women of normal values. Even Wayne struggles with these values.
He tortures Joker by beating him savagely in a moment of desperation. It doesn't work out as he expects. And he promptly goes off and invades the wrong country...err, rather he goes to the wrong building. He devises a system of super surveillance to catch this master criminal but even he doesn't trust himself with this power and leaves it to a subordinate in his mission, a man of wisdom and conscience greater than even himself. He allows a city to lie to itself and to apportion ridiculous and extraordinary powers of detention and thus subvert due process so that its people have a chance at hope, a path that can only backfire on itself spectacularly when the lie is exposed. (I always found the Platonic concept of a noble lie disturbing, even if I have rather less faith in human beings capacity for decency and a determined course of progressive advancement than many. I preferred Machievelli's satirical approach to governance and manipulation to Plato's cynical abuse of same.)
The message here: if even Batman can't walk the line between what is right and wrong without sometimes straying, without sometimes going too far in the pursuit of what is just and decent and good, even if he won't ever compromise on those values (for example he personally only "kills" Raz, and it can be argued a few faceless henchmen plus one important character, in the course of the trilogy and saves even the Joker), then what chance do the rest of us have with what we have to work with, petty, divided, and ambitious human beings of opportunity.
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