I will say that, what irritates me the most about the slavery convo is that no matter what, you're railroaded into fighting with him about it no matter your race.
Yea, there's an option where you basically say you guess he has a point.
Yeah the option to see his point comes after you're forced to jump down his throat about it. You get three options, and all three are to start the fight with him.
Here is how I approach the conversation (yes, some head canon is involved...)
For the first option I pick "You don't question it?" While the tone from the IQ is harsh, I look at it as being surprised to hear that from Dorian, who, up until that point, has seemed like the type to question everything. So I can, in my mind, place more emphasis on the "you," to have "You don't question it?" and append the question with, "You question everything, Dorian." This is at once a criticism and a compliment, and Dorian is then free to take my commentary on his character in any way that he wants.
For the second option I do pick the "I see your point," because I actually do. Dorian is approaching the argument from a logical standpoint, rather than from an emotional one, which I can appreciate. For a Trevelyan IQ in particular, while southern Thedas doesn't have the blatant slavery that Tevinter does, it is hypocritical to assume that the poorer masses are so much better off with their technical "freedom." Unfortunately, there are more nuances to the discussion on both sides of the issue that aren't shown in the game, which makes the options presented seem lacking.
That said, I can see how the conversation with an elven IQ would be seen as problematic, but the conversation system in ANY of the DAI games has never been so nuanced as to take those things into consideration, beyond providing the occasional extra dialog option for the player, and for the most part the NPC will respond in the same way regardless of race.
While on the one hand it can come across as "good for the NPC" for sticking to their guns, I believe it is actually more realistic that we moderate our conversation based on who we are speaking to -- people do this unconsciously every day with different types of people.