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.