Quote by Gary Francione:
Third, as a philosophical matter, this question assumes that if we were able to use animals without making them suffer, our painlessly killing an animal does not, in itself, amount to harming the animal. This is in marked contrast to how we think about humans. Yes, suffering is bad, but we view death, even a painless one, as a bad thing. We humans have an interest in continuing to live. Death frustrates that interest, which is separate from an interest in not suffering. We don’t want to suffer; we also don’t want to die. Animals, many say, don’t want to suffer but they don’t care about dying unless the act of killing involves suffering; it is the suffering that is a problem for the animal, not the killing. This idea, in one form or another , has been around for hundreds of years.
The moral intuition that we now all accept that animals matter morally, but less than humans, and that we can use animals when it is necessary to do so as long as we minimize suffering , was an idea that emerged in the 19th century. It assumed that it was acceptable to use animals when necessary because, unlike humans, they are not self-aware and have no interest in continuing to live; that is, they do not prefer, or desire, or want to remain alive. That idea, which most certainly makes us feel better about killing animals for food, was crazy in the 19th century. It is crazy now. To say that a ny sentient being is not harmed by death is most peculiar. Sentience is not a characteristic that has evolved to serve as an end in itself. Rather, it is a trait that allows beings to identify situations that are harmful and that threaten survival. Sentience is a means to the end of continued existence.
Sentient beings, by virtue of their being sentient, have an interest in remaining alive; that is, they prefer, want, or desire to remain alive. To say that a sentient being is not harmed by death denies that the being has the very interest that sentience serves to perpetuate. It would be analogous to saying that a being with eyes does not have an interest in continuing to see or is not harmed by being made blind. The Jains of India expressed it well long ago: “All beings are fond of life, like pleasure, hate pain, shun destruction, like life, long to live. To all life is dear.”  The notion that animals are not self-aware is based on nothing more than a stipulation that the only way to be self-aware is to have the self-awareness of a normal adult human. That is certainly one way to be self-aware. It’s not the only way. As biologist Donald Griffin, one of the most important cognitive ethologists of the twentieth century, noted in his book, Animal Minds, if animals are conscious of anything, “the animal’s own body and its own actions must fall within the scope of its perceptual consciousness.”
We nevertheless deny animals self-awareness because we maintain that they cannot “think such thoughts as ‘It is I who am running, or climbing this tree, or chasing that moth.’” Griffin maintains that “when an animal consciously perceives the running, climbing, or moth-chasing of another animal, it must also be aware of who is doing these things. And if the animal is perceptually conscious of its own body, it is difficult to rule out similar recognition that it, itself, is doing the running, climbing, or chasing.” He concludes that “[ i]f animals are capable of perceptual awareness, denying them some level of self-awareness would seem to be an arbitrary and unjustified restriction.” from that of a normal adult human, but it would not be accurate to say that they are not self-aware or that they are indifferent to death. We see this where humans are involved. If a human is mentally disabled and is not self- aware in the same way that a normal human is, we do not think that such a human is without an interest in life or that death is not a harm to her or him. She or he may be self-aware in a different way than others but is still self-aware in a morally relevant way so that we would regard treating her or him exclusively as a resource, which is how treat nonhuman animals we use for food, as morally wrong. In sum, if a being is sentient— that is, if she is perceptually aware— then she has an interest in continuing to live, and death harms her. It is not necessary to have the autobiographical sense of self that we associate with normal adult humans in order to be self-aware. And a humanlike sense of self-awareness is not necessary to have an interest in continuing to live.
Francione, Gary; Charlton, Anna (2013-06-24). Eat Like You Care: An Examination of the Morality of Eating Animals (Kindle Locations 1045-1046). Exempla Press. Kindle Edition.