Which I found to be inappropriate for the character. Especially considering the ensuing fight destroys a lot of stuff in Smallville.
You can't just have a character act one way with no reasoning behind it whatsoever, this isn't the comics. It's like him killing Zod, that will be the event that causes him to take up his "no killing code", it obviously had a great emotional impact on him. You need to explain why he has that mentality, and I think developing it off that event is a great way to do it.
By the same token, Superman will eventually develop to where he doesn't have emotional breaks like the one he had against Zod in defending his mother, but in character development, you need to start at the beginning and work your way to that point. This was his first time putting on the cape, he'll get there.