The selling of slaves...
In some parts of the world, this practice was allowed because of historical reasons and local politics.
In these areas, it became part of society, with laws in place to manage the rights and duties of both sellers and buyers.
The main reason for permitting this practice was the economic benefits and the tradition of keeping a structured hierarchy within sects. It helped sects manage their resources better and facilitated trade between different sects.
Central World State was famous for allowing the buying and selling of slaves, to the point where it was almost worshipped.
Legally, it was justified, and the nobles who were keen on acquiring slaves supported this idea by claiming they were improving the slaves' lives by providing them with food, water, and clothes. To these nobles, slaves were seen as little more than livestock──useful for labor, sex, or even as expendable resources in battles.