While I haven't watched Man of Steel, I feel the need to show my inner weeaboo and say that the anime Trigun is probably the best fictional analysis I know of the "Thou Shalt Not Kill" thing. The main character, like Superman, is incredibly overpowered and refuses to kill. Interestingly (and spoilers, if you care), he is faced with an even more extreme situation near the end than Superman was--a truly irredeemable villain mind-controls villagers who are about to kill the main character's surviving companions, and he even begs the main character to kill him. He does, and then spends the entire next episode angsting and hating himself for breaking his code, even concluding that he was wrong to kill and should've been able to find an alternate solution. Which, honestly, I respect a lot more than "Oh well, guess killing's not so bad after all!"