A strong case can be made for the view that animals, even much simpler animals, are intelligent and capable of basic feelings. Fish, for example, seem able to reason transitively, and they certainly behave as if they are subjects of pain and fear. Given that this is so, do they deserve the same level of respect as we do? Ought we behave towards them as we do to other humans?
Here is a thought experiment that strongly suggests that the answer to both of these questions is 'no’. Suppose you are walking along a path by a cliff and see you a man trying to keep his balance on the edge. Over his shoulders is a long taut rope. As you get closer, you see that dangling from one end of the rope is a small child holding on for dear life. On the other end is an equally desperate dog with its teeth biting hard on the rope. Putting to one side your astonishment at the situation, you rush over to help, but it quickly becomes apparent to you that you (and the man) together will only be able to pull up one of the two creatures, and that in doing so, you will condemn the other to a deadly fall down the side of the cliff.
What ought you to do? What is the right thing to do? The answer seems obvious: you should pull up the child. That is the right thing to do.
Imagine now that there are ten adorable puppies on one end of the rope and a single child on the other. What ought you to do now? Again, the answer seems obvious: you should pull up the child.
What if the animal(s) let go will suffer terribly at the base of the cliff before dying and it is somehow manifest to you that this will occur? Does this make any difference to what you should do? More fantastically, what if there is a child one side and a hundred dogs the other? Or, in place of the dogs, ten thousand fish in a large tank attached to the rope (on the assumption that fish can feel pain)? There will be much more pain in the world, let us agree, with the deaths of the dogs (or fish) than with the death of a single child; for the child, let us suppose, is without parents, a castaway whose death will impact hardly anyone. Does the realization that all this is the case make any difference to your assessment?
I think that it doesn't. If you agree with me, and I think many of you will, you are agreeing that is simply isn’t true that we ought to treat animals with the same respect as humans.
Interesting further questions arise here. Suppose a human is dangling on one side of the rope and an equally intelligent Martian on the other. Who should you pull up now? The human, I would say. But what if you yourself are a Martian? Then you will say correctly, it seems, that it is right to pull up the Martian.
This suggests that what is right and wrong is relative to an index or context of evaluation. What is right relative to one context can be wrong relative to another. This doesn’t make right and wrong subjective. After all, weight is relative to a context of evaluation too. Given Earth as my context of evaluation, I weigh 170 pounds. Given the moon, I weigh about one sixth of this.
Does the thought experiment give us license to conclude that we are morally free to do what we like with nonhuman animals? No, it does not. Nonhuman animals experience pain, and fear and anxiety, as we do, and we should do our best to minimize these negative mental states in our treatment of them.
Perhaps what we need to do is simply to change the ways we treat animals before we slaughter them. But even if we then cause them no pain or fear (or at least very little) and we increase the amount of pleasure they feel, still we are unnecessarily shortening their lives and so causing them to forego future pleasure.
The fly in the ointment for this reply is that many of these animals would never have existed at all, had it not been for our desire to eat meat. Is it then unjust for us to have brought them into existence in the first place – if indeed we treat them well throughout their lives?
The reality is that many of the animals we eat are treated abominably and capitalism being what it is, this is not likely to change any time soon. So, it is tempting to conclude that we should be vegetarians, at least until such time as our actual practices in raising, feeding and slaughtering animals change, unless we can be assured that the particular animals we eat have been raised and live in a very humane environment.