Another one of these. Goody protagonist doesn't lay a hand on women both they and the plot have consented that it's in his best interest to fuck them. Meanwhile the antagonist rapes whoever he feels like.
This is either the author's ntr rape fetish or some commentary on masculinity. Either way...
A result of slavery being used as a fetish point to sprinkle in rather than actually contribute to the story. The only one it makes sense for is Kaede, the rest is handing it out like candy for the sake of adding to the MC's "slave harem".
If it looks like shit, smells like shit, and tastes like shit, then looking off for the sign that says "this isn't as shit as you think" isn't going to help a whole lot with the negativity. If you want to know more then you go into locked threads on the forums to dig for conflicting staff...