Fatwa 64, which effectively justifies the systematic rape of women and girls, says it is necessary to set out rules because "one of the inevitable consequences of the jihad of establishment is that women and children of infidels will become captives of Muslims".The confusion is easy to fall into. Aristotle himself says that justice is lawfulness plus fairness, to paraphrase very loosely, and it can thus kind of sound like obedience to the law is a good in and of itself. But that isn't really what he means: on a closer reading, he means to say that it is good to obey the law if the law is properly structured.
Among the disturbing list of rules are that 'owners' of mother and daughter captives, or sister captives cannot have intercourse with both and that owners and their sons cannot have intercourse with the same woman captive.
They also state that owners should not cause the captive women to abort if they are pregnant, should not sell her to an owner they know will treat her badly and should treat her with "compassion"....
In order to deal with the women captured by fighters, IS has established a department of "war spoils" to manage slavery.
Now the laws in their enactments on all subjects aim at the common advantage either of all or of the best or of those who hold power, or something of the sort; so that in one sense we call those acts just that tend to produce and preserve happiness and its components for the political society. And the law bids us do both the acts of a brave man (e.g. not to desert our post nor take to flight nor throw away our arms), and those of a temperate man (e.g. not to commit adultery nor to gratify one's lust), and those of a good-tempered man (e.g. not to strike another nor to speak evil), and similarly with regard to the other virtues and forms of wickedness, commanding some acts and forbidding others; and the rightly-framed law does this rightly, and the hastily conceived one less well. This form of justice, then, is complete virtue, but not absolutely, but in relation to our neighbour. And therefore justice is often thought to be the greatest of virtues, and 'neither evening nor morning star' is so wonderful; and proverbially 'in justice is every virtue comprehended'. And it is complete virtue in its fullest sense, because it is the actual exercise of complete virtue. It is complete because he who possesses it can exercise his virtue not only in himself but towards his neighbour also; for many men can exercise virtue in their own affairs, but not in their relations to their neighbour.Emphasis added. Law is justice insofar as it commands the behavior that virtue itself would command. In that way, obeying the law is complete virtue from the perspective of your neighbors: though it does not insist on your virtue in private matters, where neighbors are concerned, a rightly-formed law mandates that you act rightly toward them.
ISIS clearly thinks it is doing something moral here by regulating away the worst practices of its fighters, and thus mandating that they treat the women they take as slaves with 'compassion,' both while raping them and at other times. In fact, they have codified the worst abuses into the law: the slavery and the rape themselves. Now the law will permit them to feel good about themselves for avoiding a few bad practices in the performance of their monstrosities.