Steven Den Beste has a fascinating article on the ethics of owning slaves programmed/brainwashed to desire slavery, motivated in part by musings on the ethics of owning sentient computers in the future.
(Personally, I’m not sure that day will ever come, and I’ll be more inclined to worry about it when it actually happens or looks close to happening. Let’s talk after someone produces a computer with the sentience of a chimpanzee.)
He is slightly off, though, when he says:
And it is hard to see how the eventual owner of such a voluntary slave could avoid carrying any of the ethical stain. I think it would also be immoral to own such a slave.
On the contrary, in a society with a permanent slave class, it is entirely possible to own a slave honorably. As an ethical slaveowner, you will treat your slaves better than the slaveowner down the block will, and since the poor slaves can’t escape their condition in any meaningful way, the best the slaves can hope for is for you to keep them. Such rationales were used by many antebellum Southerners who kept slaves, on the theory that free blacks were very likely to be kidnapped and re-sold into slavery (something that did happen far too often).
Of course, such an ethical slaveholder would also work like mad to abolish such a horrid institution as a permanent slave underclass.
Similarly, here’s how you could keep a sentient slave programmed to want subservience in an ethical manner:
Write a contract freeing the slave, but make the contract conditional on the slave’s acceptance of the deal. Sign the contract, and give the paper to the slave, complete with space for him/her/it to sign. From that point on, treat the slave as a full-time, live-in employee. This improves the slave’s conditions to nearly perfectly mirror those of voluntary employment, and give the slave the power to confront his/her/its tendencies towards subservience at his/her/its own pace.
We don’t need any such gyrations in current society because slavery of any kind is currently illegal and/or impossible, which is clearly the optimal ethical case. For suboptimal cases, though, there are often hard problems and trade-offs; failing to respect those can create new injustices.