In the final confrontation with General Zod in *Man of Steel*, Superman breaks Zod's neck just before Zod kills some humans in the corner of the train station with his heat vision.

After breaking Zod's neck, Superman screams in agony.

Why is he agonizing?

Is it because he was forced to kill Zod when all throughout the movie he was a pacifist? Or is it because he realizes that he has also killed the dream of his father to be a bridge between humans and Kryptonians?