Probably giving it more thought than anyone in the writing team did, but taking slaves from war doesn't really mean they're only enslaving defeated enemy combatants. And frankly there's no way that's the case, not only because we're ultimately talking about a slave society, but also because we're talking about one whose numbers are boosted in a significant way by the slave population alone (as pointed out by Brienne).
But again, looking at shit like the grooming people, it shouldn't have even surprised me that evil orcs taking slaves from raids and honorable minos taking slaves from war(=raids, sieges, and all that shit) is an unironical angle. Like, if that's the line then might as well let Kaz win. Girl would have her work cut out to make things worse, that's for sure.