While Batman has famously refused to kill any villain he encounters, even indirectly, often putting himself in harms way in order to save someone who might not deserve being saved, there's one type of villain who has a unique loophole that makes Batman entirely OK with killing them.

When Bruce Wayne lost his parents that night in Crime Alley, it traumatized him to the point that he never wanted anyone else to suffer the type of pain that he did. Even though criminals may hurt people or may even be monsters, they may still have children of their own or their own loved ones and Batman never wants to put someone through that pain, which is why he goes out of his way to save everyone Gothamite he can, even those who don't deserve it. Bruce's father was also a doctor who instilled in his son the idea that all life is precious, this only furthers the idea in Bruce's mind to never take a life, but one group of villains are immune to his rule.

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In Scott Snyder and Jock's The Batman Who Laughs #2 Batman is fighting against a demented version of himself that's been fused with the Joker. During their encounter Batman says to him in no uncertain , "You won't win. I will kill you if I have to." To which The Batman Who Laughs simply responds with "Kill me.... Because I'm you, it doesn't count? Free ?" which shows that Batman is perfectly OK with killing villains, those villains just have to be evil versions of himself. While Batman never actually ended up killing The Batman Who Laughs (that honor went to Wonder-Woman), the fact he threatened it at all is still quite a shock.

Batman Won't Hesitate to Kill... Himself

Batman Who Laughs, a sniper-rifle wielding Batman is shown as the Jokerized Batman narrates.

This shows a rather dark path in Batman's logic; he won't harm genocidal maniacs like Joker but is perfectly fine with "killing himself." While Batman has expressed self-destructive tendencies before (such as when he gave up the entire idea of Bruce Wayne during the Bruce Wayne: Fugitive arc by Ed Brubaker and Scott McDaniel), none of those tendencies are quite as dark as threatening to kill an alternate universe version of Batman, even if they are fused with the Joker. Batman was able to eventually subdue The Batman Who Laughs with non-lethal means, but it doesn't bode well for any other evil versions of Bruce Wayne out there, should they ever push The Dark Knight too far.

Bruce Wayne has saved a lot of lives in his time as Batman, a lot of people and villains have been saved because of his no-killing rule. However, it seems the one life Batman has absolutely no problem ending—is a version of himself.

Next: Joker Isn't Gotham's Scariest Villain, According to Batman