So in a nutshell, we can say Superman's appearance, how he and Zod destroyed all of those lives, THAT'S what turned Batman into a branding, killing Bat? It wasn't even in Gotham. An employee or maybe it was many employees (we don't know for sure) went down that day. Im sorry but if he looked into it more, he would find out that is not just Superman's fault. Superman also saved lives that day. Yes he took part in the destruction. It's a part of his responsibility, but if Bruce used his head, he would know that Superman didn't intentionally kill those people. He didn't want them to die. Why would BATMAN of all characters throw away his moral code because there was an alien invasion in Metropolis? Does he toss his code away everytime a huge terrorist attack happens? If he had some employees working in the towers during 911, would he go on a killing spree? Come on man.
There's no history shown or told to us. He's just there as Batman. Been doing it for a while. Experienced loss like the versions we've seen in the comics or films. And then this Superman stuff goes down, and he's suddenly a monster who has thrown away the entire point of Batman. It's forced. It's done so there could be a scene towards the end where Superman inspires Batman to go back to his old ways. It would have been better if he was just brooding, and more depressed, but still acted like himself in important situations. Then he's about to kill Superman, and he doesn't. Then right after this, he continues to be the Batman he used to be. But this doesn't happen before the murder that almost took place in that abandoned building, and it doesn't happen afterwards either.
I personally don't think it was the Superman thing that sent him over the edge. I don't believe he killed his enemies post-Superman. He was already over the edge, and he let himself go over the edge from the same things that comic book Batman or even Bale's Batman went through. They endured. This one didn't because he was written to be weak, so they can make him look stronger later when he goes through his "arc". For me, it made him look weaker by the end of it.
I can tell Terrio never read a comic before this movie, because everyone is out of character.
Batman stops being interesting when you take away his heart and his code. This movie did both.