Do you find D&D does this with other aspects within the game such as victims of murder, the family of those murdered, victims of theft, victims of arson, victims of betrayal, victims of brainwashing, victims of fire...etc?
Oh for the love of...
Why is it always the same slippery slope? Because there are so many bad things in the world that we cannot distinguish differences between them and thus must somehow ban all bad things. This argument is farcical and unserious: no one wants to ban those things because, in most instances, they come in places that seen as justified. And that's not to say you can't have those elements done badly and anger people because it's not hard, but people are often willing to overlook that stuff on its face with the right justification. Those don't exist for things like slavery and sexual assault.
Similarly, things like slavery and rape often disproportionately effect certain people and thus are more likely to make them specifically feel less welcome. This isn't an instance where anyone can have a phobia, but rather specific groups are going to feel uncomfortable because of these things.
Honestly, I feel all you're doing with your individual/culture exceptions, your genre exceptions and now this respect requirement is shifting goal posts with your criticism. I have no interest in discussing this topic within a sea of ever-changing parameters, exceptions and requirements.
I thought the pushback against controversial content, specifically slavery, was due to how recently slavery existed within US history and how it may affect black RPGers. This other stuff you're bringing up, to me, is frankly noise.
It's not a shifting goalpost, but part of the actual point: how it affects people of color is because the implementation of these things in a game are often shallow and cheap, being used as a tag for the players to know someone is evil. You're taking a horrifying practice that tore apart entire cultures in the real world and turning it into an optional sidequest. Honestly, in the Dark Sun thread someone pointed out how many times slavery was mentioned in Wizard books, but has any book looked at it as anything other than a side-detail? Because I can't think of any. And that's the point: it cheapens impact of the real thing as it never actually engages with it.
Seriously what are you going on about? I said inspired by a period of humanity's history. No one ever said that every species is a slaver? Also to note many of the D&D worlds have predominantly human populations in comparison to other species or at least are the dominant species (FR, Greyhawk, Mystara...etc) And many non-human species within D&D are or have been slavers. Some feast on intelligent life forms. Others use them for sport.
You're missing her point in your indignance: @Faolyn isn't talking about every species being a slaver, but rather that why should slavery be so widespread and used so often if this is meant to be fantasy, and why is slavery such a thing being consistently carried across as an "inspiration" from history compared to most other things when it's often relegated to being a completely trivial detail ("Oh hey, and smuggler also trades in slaves")?
We often don't carry over other details in history that would require a great deal of explanation: differences in languages, the limits on freedom of movement for people, taxation, etc... all these would almost certainly impact a setting and give flavor more than the current implementation of slavery in 5E, and yet they never get the same sort of defense.
The point is that something as incredibly impactful as slavery needs the same sort of explanation and understanding (if not moreso) and yet never gets it. That's what offends people: it's not part of the setting outside of an easy way to tell you how bad a bad guy is. It's never necessary except as cheap set-dressing. Now, if you make it not that, good on you but that's not what is being criticized here: people can handle such things much more easily in groups they know in a personal setting. And even if they didn't, there's only personal risk in that. It's not a major company meant to appeal to a large part of the audience and trying to be more welcoming to a more diverse audience.