lol, blackwood company had multiple races.. remember?
the dunmer people didn't stop slavery, it was that one king. and even then they still continued to slave other races..
I can already tell that your comment is biased, as you love dunmer, and my comments and mind are biased, as i love both beast races.
and ( jackie chan uncle voice ) ONE MORE TING
the Argonains didn't sell their own kind to slavery, some did , but Dunmer kidnapped beast races that were travelling and slaved them...
and i agree, Argonians aren't " innocent " its just that Slavery to our minds ( and i mean us as humans, not RP a Game Race ) is seen as a really really REALLY evil and bad thing
This will be a long post so get comfortable as many people on this forum, especially the OP, seem quite ignorant of the Lore. Which is really not all that important except for when someone is trying to generalize in the games lore and is wrong. If you want to hate on a fictional race at least be justified in your reason for doing so.

Now I am not saying you are ignorant, just ignorant of the inner workings of a fantasy world that does not exist and is based on a video game. Hardly something to get offended over. However I cannot think of a better word for ignorant so I apologize if that sounds rude.
Who do you think helped procure the Hist? The Argonian members... Who endorsed the use of the Hist? The Argonians did not seem to object to it.
Two Great houses, ironically Hlaalu and Dres fought Indoril and Redoran in a bloody civil war over the issue of slavery. Redoran and Indoril were very temple based houses. They were defeated and slavery was abolished in Morrowind prior to the events of Oblivion and at least several years prior to the Red Year. There is no evidence slavery continued as an institution by any of the Dunmer other than maybe some rogue slaving parties who could probably not forget the traditions they lived with for centuries. That surely does not excuse them though. I think the only evidence of that is a rumor in Oblivion too. Which also happens to be one I never heard. I don't really doubt it but could you provide proof that the Dunmer did indeed continue sending slave parties to Black Marsh? I cannot seem to be able to find it.
I am not being biased at all. Lol I really like the Beast races. Hell I think I like every race for the most part, well except for those Altmer scum...jk the Thalmor svck but the Altmer are pretty awesome sometimes. Since I like the Beast races and the Dunmer specifically I look at it from a more neutral standpoint.
Look up the lore. Seriously, it is all there. Yeah the Dunmer did bad things but not all of them did. In fact most didn't even participate in slavery. Some actively fought against it in Morrowind. It was mostly just the great houses and the temple instigating their old outdated traditions. I am not saying the Dunmer are saints by a long shot but people give them a hard time that some of them deserve but then pretend the Argonians and Khajiit are all saints when they are far from it. They are all equally capable of being bad and good.
Hell, there are rumors the Argonians started the Knahaten Flu that wiped out whole races and entire cultures in Black Marsh. The Kothringi, silver skinned humans and the Lilmothiit, a vulpine(fox-like) beast race, as well as several others. http://www.uesp.net/wiki/Lore:Pocket_Guide_to_the_Empire,_3rd_Edition/Argonia Scroll down about 2/3 of the way or read all of it. The only species that survived was reptilian in nature. Or Argonian. Slightly suspicious. Even more so when you look into it further. Pretty bad right? That is if you take it at face value. Supposedly they were oppressed by many enemies. However does that justify wiping out everyone not of the same stock as themselves? Not at all. I mean it is said to be a rumor but when you look at all the context it is kind of hard not to think they caused it, even if I want to doubt it. Especially since most of the Argonians interactions with humans were with Pirates and such types at that time. Their solution to those threats? Genocide? But that was likely at the hands of just one Argonian. I am sure not all of them would approve of that. Though there are probably quite a few that would.
Just like most people have differing opinions the Argonians are just as capable of being bad. It is very weird to me that anyone thinks they are all goody two shoes. If they were, they would be the most boring race out there. Good and bad is what makes any race interesting. But some Argonian fans think they are these lizard folks that are all oppressed and such sad sob stories with hearts of gold. Nope, they are just like everyone else except they are lizards and worship sithis worshiping trees that can control their minds from time to time if they are within range. Which is a very interesting symbiotic relationship, but it begs the questions of how the Hist view the Argonians, as tools or as children? Whether the Hist care about anyone except the Argonians and even if they care about the Argonians? After all they would naturally hate every other race as the other races are descendents of the Ehlnofey who destroyed most of the Hist when the Hist stood to the side in the great Ehlnofey wars. This makes the Argonians the only race that is of differing descent than the others.
If some Argonians sold their own into slavery, then the Argonians sold their own into slavery. Unless you want to say since many Dunmer did not own slaves then non of the Dunmer were slavers. You want to toss that out there? Didn't think so. Besides it was an entire species of Argonian.
"Archeins: During the era when other races tried to put plantations in Argonia, Archeins were very powerful, and made fortunes by selling other Argonians into slavery. Since the other races realized Argonia is unfit for plantations, they have gone bankrupt."
To further that, to say all Dunmer had slaves or even supported slavery is being willfully close minded. They didn't. It was an institution that was heavily enforced by the Great Houses AND the Temple. Most were indoctrinated by that system just like certain unnamed religions and goevernments in our world created the idea of race and encouraged the enslavement of other "Lesser" races. Do you blame the culprits or the victims? There are two classes of victims there. The ignorant and the abused. The common Dunmer were ignorant and the Argonians AND others like Khajiit were the abused. I will let you guess who the culprits are.
Personally I think Genocide is worse than Slavery but both are obviously bad and really you cannot hold a race accountable for something a member of their race did. It is not like it is their fault. Unless of course it is and then kill em, kill em with fire! Errr, might want to try lightning on the Dunmer.
Dear god that was a book. Hope the 3-4 of you that actually read through it enjoyed it.
TL;DR, everyone, even the downtrodden beast races are capable of being good and bad and that is supported by Lore.