> Secret orders may be a necessary evil; but secret legal justifications? What could that even mean??

The argument is that by disclosing the legal justification you give information to the targets. For example, if the argument for allowing a drone killing required an explicit threat to commit a violent crime by the target, targets could know what to keep their mouths shut about in order to avoid qualifying. It's a weak argument. But hey, maybe they can keep that argument secret too and then no one will be able to challenge it.

That argument is beyond weak. It sounds to me like it's saying "don't tell someone what the law is so that they'll be more likely to break that law, allowing you to kill them."

If there's a law that's punishable by death, it better be publicly known.

That argument sounds rather dark, as the same thing which illuminates the criminals -- guess what -- also illuminates the people. And journalists, lawyers, and associations that digest information for the people.

So now the overwhelming majority of the world goes dark on the law because a minority of uniquely dangerous criminals are lawyer-like Westboro Baptists with bombs.

If terrorists wish to confine their behaviors to the technicalities of western law because they would rather get arrested than shot, that is actually a highly desirable outcome. We should seek to capture all criminals alive and decently, and gather what data they have to attack other networked crime. Seriously, law-conscious Westboro Baptist terrorists would be a positive development.

This is no different from a criminal learning about the circumstances in which a cop might shoot them, and thus opting to drop their gun in certain situations. The criminal is being more legally conscious as part of their strategy.

While wrongdoers who play legal strategy can be a frustrating nuisance, but the alternative is secret legal memos, which I find more frightening.

For the same reason that we don't accept secret laws, we shouldn't accept secret "legal justifications."

Perhaps the legal justification needs to be abstracted from specific cases. Only if a specific case fulfills the justification can that justification be used in secret prior to full execution of that move which then requires full disclosure in post mortem of the event. A non-indefinite yet reasonable time limit should be another requirement that forces either rescinding the justification and/or requiring full disclosure.

This way a justification can be made without details being made public that would alert a sensitive target. It is also necessary to make sure that a potential authorized kill could not be held open indefinitely and the details released publicly in a timely manner.