A PBS documentary comes to mind upon reading this post. There is a type of ant which keeps a type of aphid in its anthills. They essentially milk these aphids the same way humans keep and milk cattle. Or maybe its termites and spiders or something, I forget. The point is that there is a non-human species who, in effect, keeps slaves. If we consider “Well, nature does it!” an adequate barometer for human morality, there ya go. Slaves are ok.
Now, as to the word slave. It has certain meanings, but I think the one the OP intended is that of animate property. This means that the owner of the item is the final arbiter of what can and can’t be done with that item… up to and including its destruction. If I had that kind of ownership over a human being, it would be my ‘slave’. If I had it over a monkey, it would be a ‘pet’ or something. If I had it over a plant or a car, it would just be a ‘thing’.
The concept of being cruel to a human is clear. You can’t whip a human. UNLESS that human is a slave. Then it’s still cruel, but ok. Well, socially, at least. Not that I’m condoning slavery or whipping people or anything here, please, just stick with me, I’m building a metaphor!
The concept of being cruel to a car is rather absurd. There’s a scene in the british sitcom Fawlty Towers in which Basil, frustrated, grabs a branch and repeatedly hits his car with it. NOBODY will watch this and feel bad for the car, being assaulted like that. It’s crazy, cars aren’t conscious. Cars can’t be slaves. They’re property.
The concept of being cruel to a PLANT is almost as absurd. Granted there are people who will say “don’t hurt trees” but well, that’s another story. Trees aren’t ‘slaves’ but they’re living property, aren’t they? Nobody feels bad about eating a carrot or burning a log in the fireplace. That’s life.
The concept of being cruel to an animal is, sadly, neither absurd or unknown. People are cruel to animals all the time… from the hick down the street kicking his dog, to the idiot shooting himself in the face with a potato-gun-launched frog. Some people feel bad about hurting animals. Others think the animals are there to be hurt.
Well, ok, then… for which animal is it considered ok to hurt them, and for which is it considered barbarious? Usually it’s ok to kill and eat the stupid, ugly, or just really really tasty ones. The cute furry ones become ‘pets’. The ugly ones (lab rats, anybody?) become ‘items’ again… it’s ok to destroy them, they’re just things.
So it’s ok to eat a lobster, or inject a lab rat. But it’s not ok to kick a dog, or eat a monkey. People choose which ‘things’ are to be treated which way. And different people have different ideas on how to treat different things.
My summary: Cute animals are not slaves. Ugly animals are. And if aliens show up, we’ll make GREAT pets. I hope we don’t taste good.