Fantasy and Realism in Art
Worldbuilding is, first and foremost, a creative and artistic Q&A forum. Our purpose, specifically, is to help solve any problem a worldbuilder might come across in their creative endeavour (of course, within the scope of SE and forum rules, customs, etc). Our querents are often writers, but we also have game developers, hobbyists, composers and others whose projects involve understanding and manipulating complex concepts ranging from orbital mechanics to sophont social behaviours to cosmology and theology.
We accept queries about slavery, just as we do about torture, reproduction, abortion, imprisonment, dark magic, and a whole host of other creepy concepts, simply because these are legitimate areas of study for the worldbuilder. Not every story will involve such things, and not every world will need them. For example, Tolkien got along with his story pretty well without dwelling on the minute aspects of a torturer's or a slave's every day schedule or condition of living.
That said, some stories do dwell on the conditions and lives of slaves. Off hand, stories such as Spartacus or Gladiator do. Movie franchises like Saw require knowledge of torture (instruments and their uses and effects), dark psychology and so forth. Other stories explore various aspects of the human condition, and often the bad ones at that, in order to speak out against a contemporaneous or historical evil. In order to do this well, the author needs to know what actually went on, how life carried on, and the nature of the phenomenon being written about.
As an art form in and of itself, and as an adjunct art that informs fictional writing, movie production or game development, worldbuilding needs to be free to explore these concepts so that the artists who produce fictional worlds can understand how these concepts come to be and how they function within society. It's our job to help the worldbuilder solve those kinds of issues, taking into consideration and tailoring our responses to the specifics of the worlds, cultures, histories, and biologies of their particular settings.