I'm going to assume nobody is reading this that has yet to watch
Man Of Steel, but just in case, SPOILER WARNING. So at the end of that movie Superman is forced to snap General Zod's neck in order to stop his rampage. The decision was met with a lot of backlash from the fan contingent that is of the opinion that Supes would never take a life. At the special
Man Of Steel fan event that was held last night Zack Snyder addressed this.
"It's a real world problem. I think the effect on Superman, it is a deeply difficult decision for him to make," the director explained to host Kevin Smith.
"It's not a thing that he takes lightly, and you can see it affects him pretty profoundly. And maybe we'll see the repercussions of that in the next film. How that's affected him, making that decision… Maybe." I think we can take that as definitely! Snyder is just being cagey about revealing too much. He goes on to address the "unwritten rule" about Supes killing, and rightly points out that he has done so..a few times!
"Well, what's funny about that rule is that it exists in the movies," he said.
"But it doesn't really exist in the comic books. He's killed Zod a couple times in the comic books. Killing General Zod is a practical solution to the problem. He wouldn't let his personal aversion to killing cost the lives of an entire planet or those little kids, that little family. So if he had said, 'I'm just morally opposed to killing so I guess I have to let him kill those people.' Those are the dilemmas. We set that up directly so there would be no solution other than that solution." More at the link below.