There’s an interesting post and discussion on What Sorts of People Should There Be? on he philosophical basis for according rights to severely cognitively disabled humans while denying them to intelligent animals such as dolphins and apes. Joseph Singer has argued that such a distinction is a speciesist one, and that in order to avoid speciesism we must simultaneously lessen legal protections for people with very low IQ scores while heightening them for intelligent animals. There are a number of potential objections to Singer’s argument, as the original poster points out, but it is somewhat more difficult to come up with an alternate one.
Here’s my take, which I originally posted as a comment on WSOP (since-added thoughts in italics):
I actually struggled with this question since I identified as an animal rights advocate before I identified as a disability rights advocate, but still believe that it is less horrifying for people to eat cows than for people to eat cognitively disabled infants. My reasoning has gone as follows:
I consider myself a being worthy of moral consideration and good treatment. I know that at some point in my life, I may lose many cognitive functions, potentially even to the point where I am listed as “profoundly” cognitively disabled by Singer’s terms. The thought of losing moral rights at this same time horrifies me. The reason it horrifies me is because my sense of continuous personhood is not based on my ability to do complex tasks but on subjectivity. If someone hurts me, I rarely think to myself “it is so wrong that this person is hurting me. Does this person know the kind of higher-order reasoning I am capable of?” I think “ow.” Higher-order thought, like “use of tools,” “advanced technology,” and “ability to form abstract moral judgments,” seems to me to be only relevant as one of those post-hoc rationalizations for privileging an already-privileged group that appears to have a monopoly on a particular trait.
I am assuming (for lack of proof to the contrary) that people who become cognitively disabled continue to have emotions and feel pain in the same way they had before. There is also no reason to make a distinction between people who become disabled and people who were born disabled, since what matters is not that there *was* ability in the past but whether there *is* subjectivity in the present, and it would be odd to assume that people who were always disabled have no subjectivity while people who became disabled have no subjectivity.
Of course then we come to the question of whether this subjectivity is shared with animals. The answer, though, is that since people do not become animals and then transform back into people as frequently as people gain (and sometimes recover from) a cognitive disability, it is harder to say exactly what it feels like to be an animal. Many animals clearly have some subjectivity and therefore deserve protection from cruel treatment, but we as a society are able to at least feign ignorance on animals’ inner lives in order to keep up the assumption that animals are somehow different from humans.
This is somewhat of an unsatisfying answer, and its grounds for according rights to people with cognitive disabilities may be troublingly derivative from the rights of people without disabilities, but I’m aiming to be descriptive, and I don’t that a dominant group has ever ended up believing another group has rights without comparing the groups to each other and finding a relevant similarity. The best we can do is look for similarities that seem actually relevant.