One of the more controversial aspects of Ben Affleck’s Batman is his use of lethal force, but he didn’t break his no-kill rule in Zack Snyder’s Justice League, despite his methods of dispatching Parademons. Batman famously has a no-kill rule in the comics and films, though his violation of the rule was part of his character arc in Batman v Superman: Dawn of Justice. Batman returned to his previous ways after the events of Justice League, and his killing of Parademons doesn’t break his no-kill rule.
DCEU non-movie material delves into Bruce Wayne’s many years of fighting crime in Gotham City as Batman. Batman never killed his enemies, though he gradually gained a dangerous rogues' gallery of supervillains, including the Joker. Batman’s descent into brutality and near-villainy began when the Joker murdered Dick Grayson (a.k.a. Robin), Bruce Wayne’s adopted son and sidekick. Further exacerbating this was Superman’s destructive battle with General Zod in Man of Steel, leading Batman to kill many of Lex Luthor’s henchmen in his quest to defeat Superman, believing that the Kryptonian hero was an existential threat to humanity.
Though not directly stated in Dawn of Justice or Justice League, Batman returned to his non-lethal and restrained ways following Superman’s heroic sacrifice, no longer using lethal force against his enemies. Justice League seemingly contradicts this by showing Batman dispatching Parademons with lethal force. Parademons are not truly living beings, however, as they lack free will and any thought outside of their service to Darkseid, so Batman’s deadly force against them doesn’t violate his reinstated no-kill rule.
Parademons were co-created by visionary artist Jack Kirby in the first issue of 1971’s The New Gods. The humanoid creatures were created to serve Darkseid and his subordinates, such as Desaad, Granny Goodness, or Steppenwolf. Parademons are fabricated or formed from tortured or dead humanoids, but no matter what their origins, the creatures are only living by technicality. Parademons have no personality, free will, or purpose, serving as slave labor and soldiers for Darkseid’s Apokoliptian regime.
Peacemaker, which takes place after the events of Justice League, features the first onscreen confirmation that Batman’s no-kill rule is in effect once again. An elderly neighbor of Auggie Smith (a white supremacist supervillain known also known as the White Dragon) criticizes Peacemaker, mentioning Batman’s rule against killing and his subsequent rogues' gallery. While no civilians witnessed Batman killing Parademons, the fact that his no-kill rule is well-known after the events of Dawn of Justice and Justice League indicates that the DCEU itself understands that Batman didn’t break his rule.
Batman’s character arc in Dawn of Justice did what previous iterations of the Dark Knight omitted by giving meaning to his violation of the no-kill rule. Batman was on the brink of becoming a supervillain in Dawn of Justice, but he reverted to his heroic ways by the end. This includes his famous no-kill rule, so his use of lethal force against the mindless Parademons in Zack Snyder’s Justice League doesn’t contradict his characterization.
