As for whether soul seizing a body would generate a sense of guilt, whether it would be despised, or whether it violated humanitarianism—in reality, these unacknowledged interstellar civilizations had no such concerns.
First, they had not signed any interstellar treaty, and their own laws did not regulate such matters.
Second, let alone soul seizing, even if Li Aozi now tricked a group of magic apprentices into becoming slaves and sold them off, even the most benevolent Song Civilization in the cosmos would not feel the slightest repulsion.
Because illegal civilizations are not protected; they are unrecognized civilizations, somewhat similar to Azure Star, the cosmos does not acknowledge them as civilized beings, as existences like themselves.