This week's Batman and Robin #8 (written by Peter Tomasi and illustrated by Patrick Gleason and Mick Gray) was a welcome denouement to the Morgan Ducard/Nobody storyline that culminated at the end of #7 when, as Bruce explains to Alfred, "Nobody's dead. Damian killed him." (Imagine parsing that statement if you hadn't been keeping up with the storyline!) As Bruce and Damian recover from their injuries (gee, good thing Bruce hasn't gotten thrashed lately in any other title), father and son talk about what happened. Bruce shares his oral diary, revealing his own desire to kill Ducard, to show Damian that the urge is natural but that he must never give into it.
Bruce argues that he adheres to a principle of not killing that doesn't "allow for exceptions." This sounds very much like a Kantian perfect duty, which is fantastic--to a degree. In an ideal world, it is easy to say "I will not kill" or "I will not lie," regardless of the circumstances, and it is an admirable person that tries his or her best to stick to them. But such a person must also recognize that there can be circumstances that will force him or her to question whether these duties or principles are truly absolute.
Take Kant's infamous "murderer at the door" example: Your good friend shows up at your door one day, frantically trying to escape someone who's trying to kill him. You agree to hide your friend, and minutes later the would-be murderer shows up, asking if your friend is about. What do you do: lie to the murderer to save your friend, or tell the truth and help the murderer?
Kant said you must not lie. According to him, you have one concern and one concern alone: following your strict duty not to lie. If you tell the truth (or simply say nothing, which will save the same effect), your hands will be clean. If you do right, you're not responsible for anything that happens as a consequence, whereas if you were to lie, and the murderer went on to kill someone else (in mistake, perhaps), you would be responsible for that.
But Kant was wrong, and he was wrong by his own standards. The murderer-at-the-door example appeared in the Berlin Press as a retort to Benjamin Constant, a French statesman, but in his more considered work, he wrote that no one can apply simple rules, including the duties one derives from the categorical imperative, to real-life situations without using judgment. For instance, even if you decided not to lie to the murderer at the door, you would need to use judgment to decide what to do instead: tell the truth, stay silent, or say "look--a squirrel!"
More relevant is the need for judgment to settle conflicts between obligations, and this provides a more reasonable answer to the murderer-at-the-door example (and much-needed perspective on Bruce and Damian's discussion). Clearly there is more than one principle, duty, or obligation at play when the murderer comes to your door--specifically, you should also help save your friend's life, based on a moral principle to prevent wrongful harm to others. I think most morally reflective people would consider that to be a more important principle in this case than the principle that you shouldn't lie. Of course, this judgment is contingent on the context of the situation: the harm threatened is severe and the lie would be to a person intent on doing wrong. In a different situation, the judgment may be different, though the two principles are the same, because the context gives the principles different relative weight.
In the second panel above, Damian essentially states the opposing principle to his father's: "But if killing them is the only way to stop them..." Bruce knows this principle well: while he says in this issue that he made a promise to himself ("and on the souls of my parents") not to kill criminals, he also made a promise that night (as seen in countless retellings of his origin) to make sure what happened to him doesn't happen to anyone else. Bruce and Damian recognize both a principle of preventing wrongful harm and a principle of not killing--but for Bruce, the latter principle always takes precedence, where I think Damian is more open to weighing the principles against each other in any given situation. (I realize this may be due to his early training by the League of Assassins, which leads him to minimize the importance of the no-killing principle. If nothing else, Bruce is helping him see the importance of this principle by adhering to it with no exceptions--the opposite extreme to Damian's dear mother and grandfather.)
Bruce does give other rationales, familiar from previous Batman stories in which killing has been discussed. He gives the virtue argument, that killing makes you a lesser person ("bankrupts your soul") and makes you no better than those you're sworn to fight. (His caution against indulging vengeance can be considered part of this, and is the clearest argument he makes; few would defend a principle based on vengeance.) He also presents the consequentialist argument ("reinforcing the same cycle of violence") that killing only leads to more killing. But note that neither of these escape the need for judgment: is your purity of character more important than saving lives, and does killing necessarily lead to more killing--or may judicious use of it lead to less deaths instead?
Bruce's continued idealism on this issue is particularly welcome following Geoff Johns' flip comments about killing earlier this week. If we give him the benefit of the doubt, Johns may have been thinking much the same as I wrote here when he said, "there are heroes that, when they need to cross that line, they do it," citing Green Lantern, Aquaman, and Wonder Woman as examples. I would just like to see more discussions like the one in Batman and Robin #8, in which these heroes defend their decisions and explain why they "need to cross that line." I'm less interested in whether or not they kill than I am in how they justify it.
Kant presented his murderer-at-the-door example in an essay titled "On a Supposed Right to Lie Because of Philanthropic Concerns," available in the Hackett edition of his Grounding for the Metaphysics of Morals. Philosophers have spilled much ink and killed many trees trying to reconcile the absolutist position given there with the rest of his philosophy; my favorite is Christine Korsgaard's "The Right to Lie: Kant on Dealing with Evil," available in her book Creating the Kingdom of Ends, which focuses on the difference between ideal and nonideal moral theory. Finally, I wrote about Batman and killing, relying chiefly on the Joker and the trolley problem (which can easily be framed as a conflict of principles as above), in my chapter "Why Doesn't Batman Kill the Joker?" in Batman and Philosophy: The Dark Knight of the Soul.