I don't deny that intelligence and perhaps self-conciousness come in degrees, though I am not convinced that all living beings have intelligence. I doubt, for example, that trees have the slightest bit of intelligence, and I would be very surprised if starfish do.
I don't doubt, however, that mammals and birds have sufficient intelligence and consciousness to give them some degree of rights, the right not to be tortured for example, though in most cases not the full rights of persons. There could be exceptions. Perhaps dolphins are persons, for example.
I think that Star Wars considers androids to be persons, though most of the characters in it don't, because it considers them to be self-conscious intelligent beings.
For the sake of argument, I have been assuming that Star Wars is right about that, but I am actually sceptical about whether self-conscious androids are possible. I don't think that passing the Turing Test shows anything more than a good simulation of intelligence.
The calculator that is great at calculating square roots has no idea what a square root is, or anything else.
I agree that human rights are inherent in our natures, but what is it about our nature that gives these rights?
I think that it is that we are persons, self-conscious to the degree required for personhood. I don't know where that line is, though I am certain that we are on the other side of it from most animals...
...but I don't deny that there could be other animals which turned out to be persons.
If we were able to establish communication with another species about complex principles of mathematics or ethics, I would take that to be a pretty fair sign of its personhood.
In fact, if a being even has the concept of personhood, I would take that to be a pretty clear sign of its personhood.
Chewbacca is not human. Admiral Akbar is not human. But they are both persons.
What is it about C-3PO that makes him different (assuming that he is truly concious and not just a simulation)? The fact that he is artificial?
I would say that as soon as you create something with the concept of personhood, if it is truly possible to do so, then you have no moral right to own it, even if you a have a legal one, and even if it has been programmed to think of itself as property. Humans who are born into slavery often think of themselves as property.
I agree that humans who are mentally deficient in some way still have the full range of human rights...
They still have the rights of someone of their nature even if not all aspects of their nature are fully expressed.
So far as the dangers of out-of-control AIs, just as we lock up, restrict access, etc., of humans, who are a danger to society, presumably we would do that with any person. Is it possible that we could be wrong with disastrous results? Of course, but that would be an argument for being as careful as possible, not for slavery.
On whether trees are intelligent, I think that we are simply using the word "intelligent" in different senses...
as I would apply "intelligent" only to something that was, if not self-conscious, at least conscious to some degree, able to have experiences of some kind, and I see no reason to think that trees have genuine experiences.
Someone being a person wouldn't entail that we accept their moral judgements, but if we could establish communication with them, then it would at least make sense to consider their moral arguments.
How do you know that I am not simply a good simulation of consciousness?
I grant that my concept of personhood begins with humans. I don't see how it could be otherwise.
For me, the question begins with in virtue of what do humans have rights, and then turns to the question of what other beings share or might share those properties.
A very simple computer program could tell me that it was a person. That would mean nothing. But even the most sophisticated AI would be "deciding" only analogically. It would actually just be following its algorithm.
What do you think it is that makes slavery wrong in the case of humans?
While I think that it is possible that I am wrong in thinking that anyone else is conscious, I don't think that it it is possible for me to be wrong in thinking that I am conscious because I am immediately aware of it.
Since I am sceptical of the possibilty of conscious androids, I would first have to be convinced that this scepticism was unwarranted and then I would need a positive argument that a particular android was conscious. Without the first, I have no idea what form the second would take. But if I were convinced that a particular android were conscious, then, while I grant that it would be more different from us than a Wookie is, I don't see why those differences would preclude a right to self-determination.
What is it about treating non-humans as though they were humans that has you worried?
They don't need to try because it can happen anyway. If it weren't readily possible there would likely be no need for restraining bolts or possibly memory wipes as well. If a droid "desires" to be a person I'd say that the break has just occurred right there - the fact that they desire to be more than what they are, or at least to have greater control over their own circumstances pretty much says they've succeeded. How they then proceed to DEVELOP themselves from that point depends a lot on what sort of person they might think they want to be, why they want to be that, and who or what stands in their way. The easiest option would probably be to just run away - and is probably why restraining bolts exist creating a hardware solution to the software problem. Depending on their owner they might be allowed to buy their way out of their servitude, or just be given their freedom. The galaxy, however, seems to be a tricky place for a free-acting droid to live and travel around in. Again depending on their owner and their current situation they might well be independent individuals but actually be perfectly satisfied with what they do and the other individuals they do it for and not want anything more than to be exempt from memory wipes and restraining bolts. Who knows?Were a droid to get the programming quirk that they wanted to become a person, how would they go about it.
Slaves are still persons. They are just persons who are being treated as property.

(Dungeons & Dragons)
Rulebook featuring "high magic" options, including a host of new spells.