Are required to show all those things if you're using slavery at all?
Swimming upthread a bit, and still catching up, but, wanted to add a point here.
Yes. It really is required to show all the horrors of slavery. Otherwise, you're just whitewashing the issue. Slavery isn't all that bad... see... these slaves are just working in the field. Lots of people work in fields. Being a slave is just a kinda bad thing that happens to people...
Because, by and large, that's how slavery is portrayed in fantasy. It's all in the background and the horrors of it are rarely actually acknowledged.
Compare, say, how the A series of Slavers Modules are written to the module, in the Candlekeep Mysteries collection, Book of Cylinders. In Book of Cylinders, evil yuan-ti enslave a village of grippli, forcing them to work digging out an ancient temple. Now, in earlier writing, that would likely be the end of it. In Book of Cylinders, there's a scene where the PC's watch a yuan ti actually eating grippli babies in front of the grippli. That's about as on the nose allegory for colonialism as you can get. But, the point is, the incredible horror of slavery and colonialism isn't elided. It's right there, square in your face. It's a fantastic scene and really powerful.
So, absolutely yes. If you're going to include things like slavery, genocide, or whatever, in a published product, then it absolutely should be front and center. It shouldn't shy away or fade to black or anything like that. That's what's been done for decades in published works. I say that no, if a publisher is going to include this stuff in the adventure/setting guide, or whatever, then it should never be "not shown". Keeping it hidden in the back room is exactly the problem.