The Zombie Rights Argument
Premise 1. If zombies are possible, then I can’t know whether you have qualia.
Premise 2. Qualia are obligation-inducing.
Premise 3. If zombies are possible, then I can’t know whether I’m obligated to e.g. refrain from torturing you.
Premise 4. My obligations can’t be unknowable by me.
Conclusion. Zombies are not possible.
P1. All the evidence I have about you is exactly the same as the evidence I would gain from your zombie twin.
P2. Qualia, said Sellars, are what make life worth living. It is a good to have the pleasingness of pleasure and a harm to have it taken away. The painfulness of pain is what makes it a harm to be tortured.
P3. Seems to follow pretty straightforwardly from 1&2.
P4. Jason Zarri has a very nice post on this sort of thing. See his “Does moral realism entail moral verificationism?” where he discusses the following principle: “Necessarily, if someone has a duty to do something, it is possible for them to find out or discover that they have a duty to do it”
This sort of argument has probably been made before. References welcome.
BTW, some relevant discussion can be found in the comment thread of this post by Eric Schwitzgebel: [link].