Is it ethical to turn Wraiths into amnesiac, can't defend themselves temporary humans? No, but it's efficient.

But it isn't efficient. If their solution worked, I would have far fewer issues with it. If they used the Wraiths' weakened states to kill them, as Buffy does with the newly risen, I wouldn't have issues with it. It's the medical experimenting and the imprisoning that I have issues with.