It's been explained to me over and over...by people who disregard the actual plot of the film and use sources OUTSIDE THE FILM to support their stance.
See, here's the thing. It's not the actual plot of the film, it's merely your interpretation of it. Most of us disagree with you and saw something totally different. Since you had naught to do with the making of said film, your interpretation of it has no more merit than anyone else's. Of course, it's possible that you're right, and Goyer wanted Supes to kill Zod and then regret not having another Kryptonian around to have a beer with and talk about the old homeworld, because that looked pretty likely.
Within the film, there is ZERO reason to believe that Clark would not kill again.
There is also ZERO reason to believe that Clark wouldn't like peanut butter and cow patty sandwiches, but I'm not really sweating it coming up in the sequels.
And believe me...it DOES get tiring seeing people who don't like Superman explain why Superman would kill and why him killing is what really makes him Superman.