Originally Posted by BlueLightning
It is not only that. Sure it could be easy to say that he was a victim of the Joker, because he really was a victim. But you have to take into account that all the mob would be again free to roam the streets, at least they would have the means to hold a grip into Gotham again, and bringing the hope of the citizens to the ground.
The thing is, I don't think Gordon and Batman became corrupted by the lie. Why? Because Batman took the fall. Instead of being something morally dubious, it becomes a sacrifice. As Gordon says at the end, he can take it, he is not a hero. He is something more. Whatever Gotham needs him to be. By definition a sacrifice is an offering, and that's what Bruce did. And ultimately, and perhaps paradoxically, that's something worthy of heroism.
I know in the context of the film, we are told if Dent messes up everyone will come after him and it's all on him but I'm not sure if legally that makes sense. They wouldn't just let the criminal go if the guy who arrested them becomes a murderer. TDKR doesn't spend any time explaining what really happened after Dent died. Who prosecuted the criminals? Did his death inspire more noble politicians? I know it's a super hero movie, so it's not a huge issue.
And about corruption, Gordon agreed to cover up Dent's crimes - that's corruption. That's not his job. He never seemed happy about it, it was Batman's choice. It takes it's toll on Gordon as we see the truth is eating him away and his wife leaving him is more proof that he didn't get away scott free.