Sorry for being Captain Pedantry, but this doesn't match at all with what I remember from my (admittedly distant in time) classics degree. Roman slaves were legally 'tools that speak', and the Greeks were traditionally credited with inventing chattel slavery. The actual treatment of these slaves varied greatly depending on role and master, from valued colleagues to expendable objects.
I have to say your apparent pedantry does not particularly match what I was taught doing ancient history and archaeology 20 years ago.
The idea that the Greeks "invented chattel slavery" is rather bizarre. It's so bizarre I attempted to find any source on the internet which might back you up, and I couldn't find a single one. What's your basis for that claim? It seems utterly ahistorical, given Greek traditions of slavery were not particularly distinct from earlier ones (that I'm aware of), except the Spartans, and the Helots were definitely
not chattel slaves, and realistically occupied a sort of status of particularly violently oppressed serfs. I wonder if it's something some self-regarding Roman author decided was true because some bloke down the
taverna told him it was, which, because it's in some surviving classical work, stills gets taught to unwitting classicists.
As for "tools that speak", well I get that Varro liked a snappy turn of phrase, but the man was seemingly obsessed with categorization and simplification (no doubt he was "on the spectrum", not that there's anything wrong with that - I'm neurodiverse myself), and I'm not terribly impressed with him insight-wise. For a man so supposedly well-read in Roman history, it's a particularly odd and inaccurate simplification. Albeit one that was very convenient for various miscreants of later eras to repeat as if it were wisdom or truth, rather than intellectually lazy dehumanization (and dehumanization is far from a recent concept - whilst it wasn't really around in the classical era, and was suppressed hard when people got near it, even as early as 1537 you have popes and the like getting mad about it).
Certainly if you regard what the Romans had as "chattel slavery" (as only one of many forms of slavery in Roman society), which is I agree how older historians describe it (less so more modern ones - the recognition of - or rather interest in - the complexity of Roman slavery has been slow in coming), then we almost need a new word for that the US and Brazil were doing, given it was something even more extreme than the Roman model. And more importantly in this context, slavery as described in Dark Sun more resembles slavery in the US or Brazil.
The thing that strikes me about a lot of these slavery discussions is how, well, American they are. I mean, slavery exists right now around the world. Historical US slavery was awful, but it was in no way unique to the US. I don't really have a solution to this sensitivity, or perceived sensitivity. It's just an observation.
The form of slavery practiced in the US is actually pretty distinct from most other forms of slavery, so I must strongly disagree. It was more similar to that in Brazil (and obviously the Caribbean), but it's quite distinct from the sort of "tapestry of slavery" of ancient Rome, or most modern-day slavery.
The racial aspect particularly is notable. Whilst the Romans enslaved entire populations, they didn't do so on the basis of ethnicity, and there was no particular thought that because your ancestors were slaves, you necessarily should be (just the usual class-based Roman sneering). Whereas the entire basis of slavery in the Americas was essentially racial in character, and this sort of "separatist", multi-generational slavery colours American depictions of slavery, including Dark Sun. Dark Sun kind of removes the racial character, only to return it in force with the Muls and the like.
So I don't that's a helpful observation or one that leads to truth, rather it's a generalization that leads to confusion. Slavery as practiced today tends to have a unique character of its own, one not really found in history. Because slavery is basically illegal almost everywhere, modern slavery has an illicit character, which simultaneously makes it more tenuous but also less honest and transparent. It's more about what people can
get away with, without the authorities noticing, than what is legal. Where basically-legalized-slavery does exist (Qatar, for example), it tends to be somewhat racial in character, dependent on deception, and to most closely resemble indentured servitude rather than chattel slavery. Hand waving as if this were the same as or particularly similar to the aggressive and legalistic chattel slavery of the US in the 1800s, say strikes me as simply misleading.
So US sensitivity seems pretty justified to me, given the insanely large scale slavery was practiced on to the point where a dead minimum of about 20% and probably much higher of people in the US have ancestors (again often known, named ancestors, not ones "lost to the ages") who were chattel slaves, and the fact that we're talking about a situation where the grandchildren of chattel slaves are still alive right now. Hell, there are people in their 40s - my age! - whose
grandparents were slaves (admittedly pretty much only where they had a father who had children very late in life, but...). Most often it's great-great-grandparents, but it's not a huge span of time.
The 'blackbirding' practise was real dark-ages stuff, violent slave raids on Polynesian islands with captives forced into cane-cutting, and that continued well into the 1890s, with the authorities largely turning a willfully blind eye.
Blackbirding was horrific, but the scale wasn't even 0.1% of the US slave trade, and it's interesting because it closely resembles modern slavery type situations in character, with the illicit nature, people being tricked into it (though as you say, force also used), and it trying to fly under the radar, as it were. I think there's a very real difference from the US experience, and that comparing it is not particularly revelatory. Chattel slavery of vast populations (perhaps 10 million survived passage, more were sent) shipped halfway across the world, and their descendants being a large fraction of the US population isn't really comparable to some tens of thousands of people tricked and/or kidnapped into forced labour (which was not permanent or generational). This isn't to say blackbirding isn't appalling, especially given how late it ran (into the 20th century as you say, and it's comparable to stuff that goes on today in a few countries), but it's a very different thing. Anyone eyerolling at the US because of blackbirding is... well... not being very thoughtful.