Yes and no. I think D&D should acknowledge the existence of slavery. I think D&D should acknowledge that there is prejudice in the world, based on race, tribe, gender, and class.
But I don't think the system should endorse these things. That is to say, I don't think women should have different stat bonuses than men.
I think Good-aligned characters should not be allowed to own slaves.
I don't think the game is as fun when it railroads the PCs by bossing them around, based on who the characters are, their gender, their race, their tribe, their religion, or their class. I prefer a setting that's more free, because then the players can feel like they have a say in their destiny.
There's something to be said for having to work for your freedom. But I just don't want to see a campaign setting so oppressive and ignorant that, socially, it's impossible for the PCs to advance no matter what great deeds they do.
I think there is some room to play with these kinds of ideas when you talk about evil-aligned realms. Maybe the PCs can go to bad places once in a while, but just like they can't always be dungeon-crawling, I think it would be tiring to keep them on their guard in a hostile land 24-7. They need a refuge.