"Man of Steel" Spoilers in this article.
I'm going to talk about the implications of super heroes killing and not killing. Super heroes being above killing was only really released as a gimmick in comics to keep all of the best villains alive, but has since gone on to be a big part of the actual characters.
In the Marvel films that proceeded "Man of Steel" the heroes were quite willing to kill.
Captain America: It makes sense that he is willing to kill in the Marvel cinematic universe despite his aversion to killing in the comics. Cap is a WW2 vet, that only recently got thawed out. It would seem rather strange that he wouldn't kill.
Iron Man: Tony has killed terrorists and villains that have gone after his life. Again, the situations of Tony offing bad guys made sense.
Thor: An arrogant prince that who is pretty much considered one of the greatest warriors of Asgard, again the act of him killing makes sense.
Soooooo....Superman kills Zod in "Man of Steel". Superman being the moral high ground is pretty much one of his defining characteristics, and I was actually fine with him killing Zod, it made sense in context to the scene. I don't think Superman should carry on killing. I think in the "Man of Steel" sequel the killing of Zod should be addressed and help shape Superman to be more in line with his comic book counterpart. Someone who will always find another way.
The act of killing Zod could really shape Superman as a force that tries to find non-lethal ways of dealing with villains, since he will know exactly how bad it is to end some one's life and live with the regret of ending the last of his kind. This could really build well as a theme through the "Man of Steel" series which could culminate in an adaptation of "What's so funny about truth justice and the American way" at some point down the line.
I think a similar approach could be used for the Batman reboot. I don't think Batman should kill, but I do think it should be implied that he did kill a few villains at the start of his career, Bob Kane style Batman.
Anyways, sorry about the general abruptness of the article.Post your thoughts in the comments.