Superman sure is the boy scout of the DC Universe, having no pride even after being so powerful, being humble and most importantly, the rule of NEVER KILLING. Except the fact that he’s broken this rule many times. Below listed are some such times when Superman was forced to kill:
Superman is forced to kill at the end of Man Of Steel where after Zod has lost all hope of his planet coming back to life, he shoots laser beams out of his eyes and tries to kill a family, Supes begs him to stop, but when he doesn’t, breaks his neck. That’s straight up murder.
Imperiex And Brainiac
Imperiex, on his way to earth, destroys everything that comes in his path, his last stop, Earth, that he wants to use as the staging ground for ‘The Hollowing’ and Brainiac, who initially sided with the Earthlings now betrayed them, Supes tries to reason with both of them but when they didn’t understand takes them to the moment of the Big Bang and hence, kills them.
The boy scout nature of Superman is nothing new to the fans, but in Injustice: Gods Among Us, the Man Of Steel kills. He, when under the influence of a drug given to him by Joker, kills Lois Lane and his unborn child, that lead to the destruction of Metropolis, snaps. And that’s bad, he starts by killing Joker and then creates world peace by enforcing it and eventually has to be stopped by Batman who brings a Superman from an alternate universe.
This took place during the ‘Trinity War’, where govt. sponsored JLA locks horns with the Justice League, this is that fight where Superman laser blasts Dr. Light’s face off his body. It is later revealed that Supes was being mind controlled, but still killing is killing.
Probably the biggest shock of all in the comics was when the seemingly unbreakable Superman died. He and Doomsday go all out, and it is in their final blow that they strike towards each other, having all their energy, which hits both at the same time with such intensity that at the end of the battle Doomsday is dead, and Superman dies a heroic death in the arms of Lois Lane.