"If sentience and cognitive ability are out and it’s a sense of responsibility that explains why parents and institutions take care of severely mentally impaired humans when we aren’t obligated to take care of wild animals, we now have a non-speciesist explanation for why we can give severely mentally impaired people rights that we don’t give to animals. It’s not that the cognitively impaired are H. sapiens, it’s that we brought them into this world—that they are of us—and so we feel like we need to protect them.
If this makes sense, it’s not wrong or inconsistent to feel more responsible for severely mentally impaired humans than we feel for domesticated animals. Which means that it can be a legitimate position to raise animals for food, even though we wouldn’t do the same to severely mentally impaired humans."
If you deny the responsibility explanation, then you’re back to human society being obligated to take care of all animals, wild and domestic, who cannot fend for themselves. As a practical matter, human society will be unable to do this to any serious extent, but that obligation will still exist and will need to be pursued as much as possible.
Even if you’re willing to accept human responsibility for wild animals, what about all those other scenarios where sentience struggles? Since responsibility does a fine job of explaining why we take care of the severely mentally impaired without giving rights to animals, let’s see how it fares elsewhere.
The sentience explanation and Tom Regan’s “inherent value” theory can’t make sense of the hierarchy of life value that becomes so stark in extreme cases like mass starvation. Decisions between who to eat in Leningrad or who to save in burning houses should be arbitrary if all that matters is sentience, but they’re not.
Responsibility/attachment explains why."
From: Forget Sentience: Here's the Real Reason We Grant Rights posted on September 1st, 2011