When Superman was blindly throwing Zod through buildings, into trains and making them explode. I'm not sure there was a single point in that fight where it was like, "Maybe I shouldn't do this because it could kill Zod." or even "Man, I should watch what I do and make sure there aren't any innocent bystanders who get hurt."

The killing of Zod would have been a huge moment if it happened in a second or third film. With so much to set-up in the first one, the impact of Superman killing someone just wasn't there. I mean, he let his Dad die to protect his secret; he's not going to kill a dude who's destroying the Earth?