You know, in real life occasionally good people have to choose between killing someone and letting that person hurt an innocent third party. This happens when a person has to sniper someone to save a hostage.
In the ending of the movie "Man of Steel" Superman is forced to kill in hand to hand a madman bent on the annihilation of all life on Earth (that goal is stated by the villain in no uncertain terms, his desire to destroy is clear). This is just the superhero version of the sniper and the hostage, the sniper being Superman, the hostage being the world.
The biggest issue people seem to have is this, "Superman does not kill." Which I do not know where they get that from. I suppose it is their own preconceived notion toward the character, that they think of Superman is boring and can do no wrong (those are in fact the complaints I most hear about the character). And I would say that the biggest complaint people have against Superman is that he manages to effortlessly solve problems, making it hard to identify with him. By having the final conflict of the film be Superman vs Audience Expectations turns out is a far more interesting fight than Superman vs Zod.
For whatever reason people expected Superman to somehow get out of the situation, I knew what was going to happen pretty much the moment I saw Zod no longer on the Kryptonian ship, his only end was going to be death. By putting Superman in a situation that he has to compromise what people feel his values to be should make him more "human" or identifiable in the eyes of the audience. I actually cannot figure out why it didn't. This is something done far better than it has been presented in the past and sets up an interesting starting point for the new series.
|And speaking of interesting starting points, go read JMS' "Superman Earth 1" which has two hardcover trade paperbacks out that have a rather cool take on the character.|
The reason superheroes don't kill to start with is because they need recurring villains. If Batman killed the Joker, then there would be no more Joker stories, and no more Joker action figure money. Superman's bad guys lack the option of being caged in an ineffective asylum so the idea of Zod being in prison is a hard idea to accept. If they wanted to they could have had the story end with Zod being thrown into the Phantom Zone, but they made a choice to have Superman kill Zod, which by the way: HE DID THAT IN THE REEVES MOVIES TOO. Zod is a monster bent on genocide, why would you want Superman to leave him alive?
If you care for more of this, here is some more of me writing about "Man of Steel" and "Star Trek Into Darkness" for good measure.