The difference between including something in your home game and WoTC including it in the official game, is the same difference as hanging a nude portrait of yourself in your bedroom, compared to plastering it on a billboard on the highway.
One is in the privacy of your home, where you have full control over who sees it and how they approach it. The other is out in the public where you have no control over it.
The difference between something being in an novel, and something being in a role-playing game is contribution. In a novel, I sit back and watch how the character reacts. If I disagree with that characters actions, then I can engage in a variety of ways. In a TTRPG I am the one deciding what acts the character takes or doesn't take. Making me responsible for those actions, even if in a small way.
Part of my frustrations with slavery in DnD isn't that it is limited to the bad guys. Because it is, and that is a good thing. No, my issue is that it is ALL of the bad guys. Have you ever taken a moment to see how ubiquitous it is?
Aboleths
Evil humans and ect
Drow
Duergar
Derro
Evil Giants
Yuan-ti
Mind flayers
Kou-toa
Gnolls
Goblinoids
Orcs
Ogres
Oni
Evil Dragons
All Genies
Kraken
Cyclops
Fomorians
Grimlock
Ixitxachitl
Kobold
Morkoth
Vampires
Liches
Neogi
Beholders
Bullywugs
Fiends
Hags
Githyanki
Lamia
Seriously if it is evil and intelligent in DnD the odds are incredibly high it either was a slave, is a slave, or owns slaves.