But we're not trying to answer that question. We're trying to figure out if, from a human perspective, crimes such as slavery and rape are wrong. The fact that morality only exists within the scope of humanity is a red herring.
No we're not debating that. Nobody here was advocating slavery nor even denying that it's fundamentally undesirable, and those here who like Tevinter don't do that because it has slavery, but in spite of it. Meanwhile, some of the moral absolutists here suggest we shouldn't like Tevinter because of its flaws, disregarding that a culture is not defined only by its flaws. If it were that, I would be unable to like any existing real-world cultures because they all have flaws significant enough to warrant criticism of these cultures as a whole.
Also, I would like to point out that our moral judgments exist in a temporal and cultural framework. The cultures of the past have made different basic assumptions about life, and future cultures will make still different ones, resulting in different moral judgments. Whatever we think of the cultures of the past now, their perspective was just as much within the human scope as ours. Future cultures may define some of our present habits as barbaric and cruel. Are they justified in condemning us? Defining your perspective as the only reasonable human one speaks to me of incredible arrogance.
My personal perspective of Tevinter is informed by the fact that I appreciate all attempts of humans and humanity as a species to gain more control of their own fate. That requires acquiring knowledge and power, both as a species and as individuals, often against the strictures religious or collectivist thinking would impose on us. I admire Tevinter culture for embodying that within the scope of Thedas as a fictional world, even while I despise the fact that the benefits of such thinking are so unequally distributed. Bioware's worlds have an unfortunate tendency to marry knowledge to evil. I do not accept the implicit presupposition therein. Give me a culture that embraces exploring the unknown and gaining control over our fates against the strictures of religious and collectivist thinking without being accompanied by evil, and I'll be there in a moment. However, I would rather be associated with evil than to accept ignorance and powerlessness as a virtue.