But let's say for the sake of discussion you are 100% correct above. Is it not acceptable in fantasy to explore non-human races that actually possess such negative characteristics in the fantasy world as opposed to reality where such negative characteristics are falsely applied to a human race?
Define "acceptable".
Also, maybe ask yourself "Is this the right question?" because I would say it is not the right question. Is it like, legal, and probably within the bounds of morality and ethics to do what you describe? I would say yes. It might push the bounds of good taste and end up raising some uncomfortable questions, but sure, it's "acceptable" in the broadest sense of the word.
But WotC and for that matter any profit-making company that isn't harshly ideological isn't just looking at "acceptable", they're looking at "attractive", "reasonable", "in good taste", and so on. Is it likely that making a race of creatures that look like people (including "ugly people" or "pretty people"), live like people (born, grow, have kids, raise kids, die, etc.), talk like people, appear to have some sort of free will and so on, but have inherent negative characteristics, and thus "need to get genocided" likely to be "in good taste"? I would suggest no. We live in a post-Holocaust, post-slavery (mostly) society. It isn't 1500 or whatever. The idea of intentionally setting up a scenario so a sapient, human-like race needs to "get genocided", even if it's "true" in-setting that they do, is not going to sit well with people, and not going to cause people to admire the company involved.
So what might be "acceptable" at a specific table, is probably not going to work for say, WotC, because it's in bad taste (and it is), it's reminiscent of a lot of creepy-ass ideology that very very very very bad people had, and it's thus not likely to attractive to well, the sort of people a company which wants to exist long-term wants to attract. Sure, 8kun or whatever would probably absolutely adore it, and the worst depths of reddit, maybe, but y'all want those guys singing your praises? My feeling is you do not. And you could bluster and say "These 8kun jerks don't get it, it's not a metaphor, it's not about the Holocaust, it's about Very Bad Monster-People!", but that won't change anything except maybe some 8kun dude will get you SWAT'd.
The TLDR of it is that you could do that, but it would be in terrible terrible taste, and it would attract the "wrong" kind of people (alongside some perfectly reasonable ones I'm sure), and would be an absolute PR disaster. A small-press RPG which was exceptionally well-written and focused and had a specific market and vibe in mind might be able to pull it off without being a PR disaster or bait for internet extremists, but as a setting for D&D? Let alone for D&D in general? Not a good idea.