The subject of Dragonlance, at least one of them, is the horror of war
The subject of Dark Sun isn’t slavery or forced eugenics.
But again, and I know we have covered this endlessly, slavery and eugenics very much are part of the core themes about man's pursuit of power and his need to fuel society having consequences. You can draw a pretty strong parallel between using people as a source of power and using magic as a source of power. And in the ancient world, slavery was a source of power that was used to fuel the growth of empires. It is terrible, as are the horrors of war, but if you are making a setting that deals with the evil things men are capable of when resources get scarce, I can certainly see why it is valid to include.
And it is set in a world that violates our own sense of morality. Which I think is an important part of what Dark Sun is trying to do. So things like eugenics being present also makes some amount of sense.
I found the opening of the first box set rather uncomfortable because it seemed to invoke that (or at least racialist science) and to invoke Nietzsche's ubermensch (which I could interpret in a way that made me feel unwelcome, but my assessment is they were reaching for something else there). Due to the history of it in the 20th century, and due to the fact that I can still remember people using these arguments to justify racism when I was young, I am particularly bothered by racialist science and I have never been especially comfortable with Nietzsche's ideas.
Pasting a passage pertaining to this here (it is woven into elements of the setting but I think the passage in the ability scores entry is actually more striking and worthy of discussion because it is alluding to this element of the setting at the very start of character creation):
I have been re-reading the boxed set (again I must emphasize very slowly so I am not 100% refreshed on everything in there yet). But one of the reasons I am also pasting the above is because when I re-read this section for the first time in about 30 years (or however long it has been since this came out), I remembered how this made me feel. It seemed ambiguous to me at first and I honestly wasn't sure what the intention was, which I found troubling. I would compare it to my first reaction to hearing the song Number of the Beast. Now that song just seems a little corny, but when I first heard it, I wasn't sure if it was just telling a story in the voice of a character or if the band endorsed Satan (obviously they don't endorse it, it is ultimately an ant-Satanic song, but the song is a story and the chorus can easily mislead you because its "666 the number of the Beast, 666 the one for you and me"). Ultimately I think what they were doing here is closer to what Iron Maiden did with Number of the Beast. And that means there is a danger it could be misinterpreted (and who knows perhaps I am misinterpreting the intention). But what I came to see in this passage was the writers using an ironic voice, and an aim to immerse you in a world that was by our standards not a moral one, which creates a sense of discomfort and unease. There is danger to that. Just like there is danger to calling your song number of the beast.
And again, I find these particular ideas surrounding racialist science to be the most discomforting, in part because they gained so much mainstream traction in society in the early 20th century and they led to so much horror (it is one of the reasons I am so troubled by the emergence of the Human Biodiversity Movement). But Dark Sun and The Number of the Beasts, these are creative works, drawing on real world ideas to achieve an effect. And to do that they sometimes need to take these kinds of risks, which I think produces interesting results. Reading through the original boxed set again, it is absolutely spectacular (visually, the way it is written, the world it creates and the ideas that it is trying to address in an RPG setting------I would say stuff like this is a good argument for RPGs as art*)
There is a similar section in the Van Richten guidebooks. Van Richten is a heroic vampire killer but he has a significant flaw as a character: he is racist towards Vistani because his son was taken by a Vistani tribe and sold to Baron Metus (a vampire who made him into one). In some of the Van Richten books, his voice suddenly switches from rationale and compassionate to completely irrational and filled with rage towards the Vistani. There is a line in one where he is discussing having a Vistani friend and says something to the effect of "I won't blame a single individual for the failing of an entire race". I think today WOTC would be very wary of including that kind of humor because it can be misinterpreted (obviously the point is Van Richten is the butt of the joke because by reversing the logic of 'don't blame an entire race for the failing of individuals' we see the flaw in his thinking: the book understands that the readers morality is the latter not the former).
*And not in the sense that it is art because it is meaningful but not playable, Dark Sun is very playable, and to me it shows you can have a clear artistic vision in the RPG medium.