There is no doubt that Kongolese is the most promising candidate south of Sahel.
I guess the issue you are talking about is human trafficking, but this kind of thing was very common in Africa at that time. This culture seemed to existe long before the Europeans arrived, and the Europeans took advantage of it. Similarly, it may not be surprising at the time that colonists intentionally or unintentionally did a lot of harm to aboriginal people. After all, long time before, human wars had already been full of profit and slaughter, even between Europeans. History is full of tragedy, but we cannot judge people in the 17th century with human rights concepts after the 20th century, or it will be somehow unfair.
We still can try not to mention these things in the game no matter what. At least I tried.