I found that claim surprising when I read your post, but it's true that a partial immunity does develop - Malaria
That said, I would suspect that if they used the malaria excuse, it was simply that.
Slavery's existed for millennia - and outside of Rome where it became an economic institution, what little I know of the subject suggests that it always seems to include demonizing and de-personalizing the victims. The whole tribe-vs-tribe mentality on every continent comes to mind, and from what I've seen, the prejudices continue centuries later, everywhere.
Sad that we as a species haven't risen above that thinking.
That said, I would suspect that if they used the malaria excuse, it was simply that.
Slavery's existed for millennia - and outside of Rome where it became an economic institution, what little I know of the subject suggests that it always seems to include demonizing and de-personalizing the victims. The whole tribe-vs-tribe mentality on every continent comes to mind, and from what I've seen, the prejudices continue centuries later, everywhere.
Sad that we as a species haven't risen above that thinking.