Agreed, there is no objective benefit to an (otherwise) advanced society in keeping slaves. But it is easy to imagine one that does because they like to. When

Agreed, there is no objective benefit to an (otherwise) advanced society in keeping slaves. But it is easy to imagine one that does because they like to. When the Maori in New Zealand heard from the English about a peaceful society on Chatham Island, 800 miles east, before two weeks had passed they set out on an expedition to exterminate all the men and enslave all the women there.