Originally Posted by OutOfBoose
Batman ALWAYS was officially an outlaw, regardless of his body count. He got some allies in GPD, but that was about it. But he would get them in any case. Remember, he worked with Gordon, who isn't afraid to step beyond the law, because he works with what he has. When it's necessary, it's necessary. More of that, police would never catch Batman. Things would be just the same.
He became an enemy number one for GPD (but not for everybody even there), because he killed a lawman and a symbol. Dent became a martyr. Police folk wouldn't take it personally otherwise. Criminal world plays dirty, why normal people shouldn't have their own joker for such cases.
I think, the only problem, that people have with murder of the strongman, is that he didn't have a kid at gunpoint. So Batman didn't have a BIG ENOUGH reason to kill him. It doesn't matter that there's a war going on.
Also, Batman behaves somewhere in the lines of the law in Batman Returns too. He doesn't carnage every single criminal he sees. I just don't get why people care about Batman's body count, when the streets are being turned into a war zone. And who knows how many normal people died that night.
The GCPD would have cared even if he didn't kill Dent. He would be wanted for the murder of Maroni, Maroni's associate and at least one crooked cop. Killing a cop is a pretty fast way to "personalize" it with any law enforcement in the world.
However, even if it was just Maroni, Gordon would still have to go after him. Vigilantism is against the law. Batman breaks that law regularly, but when written in a certain context (i.e. Gotham is dire and corrupt), one can create a scenario where some cops will give him longitude long as he stays within parameters.
You want Batman to be Frank Castle. Besides the lone vigilante with a gun was pretty boring even back during the first Death Wish film, it would make the idea of cops working with him indefensible. He is then taking the law totally into his own hands and acting as judge, jury and executioner. That makes him a direct challenge to the authority and order of the system. That means he is a threat to society.
That is one very simple reason that he is not written to act that way. Nolan just chose to challenge the principle in a dramatic way during the second film. And, intriguingly, seems to imply that Batman has given up that rule in the third film. But by that point he is no longer a nightly vigilante nor is he a secret resource for the cops.