So the existence of slavery is its own justification. Argonians (and Khajiit) deserve to be slaves because it's "just the way it is". I'm not gonna make any real world parallels, I'm sure you can figure them out yourself.
He's just spent two pages telling us that slavery is justified if a) the slaves are stupid enough to live in primitive conditions B) the slaves belong to a race that also occasionally practice slavery c) look different enough. As far as being able to figure things out goes, are you certain about that?
I'm of a people that have been enslaved to some extent for over a thousand years. Please, just because I am willing to look into a fantasy game and not wear my heart on my sleeve about lizard and cat people being enslaved, does not mean "oh har har har he's a dumb racist." And it's really childish and ignorant for you to make such accusation.
"House Dres is the only one that maintains to this day the original Velothi culture! All others have become something else. And that doesn't make them rigid traditionalists at all!" Yeah, sure.
There is a difference between cultural tradition and rigidity. The former confirms a level of loyalty, piety and honor, the latter suggests that this is done to a fault. When have the Dres been so traditional that it has hampered them?
And your contempt for the Hlaalu is leading you to underestimate them. I'm gonna quote from the 1e PGE, written in the Second Era, before the Septim Empire annexed Morrowind: "Traditional enemies of the Indoril, who have controlled the levers of government for 3,000 years, the continued resilience of the Hlaalu must inspire a certain respect." The Hlaalu always had a culture of trade and exchange. They didn't wait for the Empire to appear for this. But when it did, they seized the opportunity. They were able to use the four centuries of the Empire to rise from being the smallest and weakest Great House into becoming the largest and most powerful -- and a House that could withstand three millennia of enmity from House Indoril at the apex of Temple power isn't a house that's going to vanish anytime soon. They're opportunistic survivors. The Hlaalu-Dres alliance should be seen in this light.
I don't have contempt for something that does not exist nor did I underestimate them. I simply said what was true and what you write about Hlaalu does not contradict that. Yes they were merchant and caught a lucky break by svcking up to the Empire. Redoran wanted to meet the Empire on the border. Indoril and Dres wanted to fight them on their own terrain. Telvanni didn't care and Hlaalu said "welcome, we'll show you the way in."
Yes the Hlaalu alliance favors them more then Dres. But I don't see Dres picking up off of their own land to go die for Hlaalu's ideals and goals.
And a Dunmer slave, which surprised me. Maybe most of the slavery in Morrowind is Roman/traditional style, and they reserve the pvssyl treatment for the agricultural industry where there is profit in volume.
Obviously the Dres are not doing slavery based on race. Simply the Argonians themselves provide the largest market to buy from.