The film begins by asking: what happens if conservative law-and-order policies actually worked? The answer, we quickly learn, is that it destroys the people behind them. Without anything to fight, Bruce Wayne is just a reclusive withered husk, while Commissioner Gordon is actually going to be fired. Given that these are two of the film’s most sympathetic characters, we naturally tend to deplore this situation. And so the film’s first key point: the champions of law-and-order do not truly want to succeed at their stated mission.
I think they are in ruin because you can't build a house on a foundation of lies. Obviously Comish Gordon is struggling with the lies he told in order to preserve the memory of Dent and build legislation on the back this lie. -This taints the peace. I think that is the theme here.