Yesterday I mentioned that I don't eat octopus for ethical reasons.* A couple of readers asked why I eat some animals and not others. My rough personal guideline is that I don't want to eat anything too intelligent. I believe that chickens can feel pain and that chicken pain matters. Therefore, I think it's wrong torture chickens for fun. I also think it's wrong to torture millions of chickens in factory farms so that chicken can be priced as a staple food rather than as a luxury item. However, I don't believe that it's wrong to kill a chicken painlessly for food if the bird has lived a good life up until that point.
I just don't respect chickens very much. I don't consider them to be individuals who can have meaningful preferences about their own futures. A chicken has preferences about the here and now, but it doesn't have preferences about its future existence. A chicken isn't capable of conceiving of itself as a self over time. So, as long as the chicken doesn't suffer, it can't matter to the chicken whether it has a long life or a short one.
You might argue that the lives of chickens have intrinsic value, regardless of whether the chickens realize it. However, chickens have such simple minds that chicken consciousness pretty much interchangeable. If you kill one chicken and replace it with a new one that wouldn't otherwise have been born, the sum total of chicken consciousness stays the same. (Farming produces many more chicken life-years than there otherwise would have been.) There's not enough difference between one chicken's experiences and another's to worry about how chicken conscioussness gets divided up between chickens. I think it's morally equivalent for eight chickens have two good months vs. one chicken having 16 good months.
A complex mental life makes a creature more of an individual. At a certain point, I feel like some edible species have enough going on upstairs that the unfolding drama of each self is valuable for its own sake. As an animal's cognitive capacity increases, it becomes more plausible to think about the animal's attitude towards itself and its existence over time.
Suppose your vet tells you that your elderly German Shepard needs an expensive operation that will prolong her life for 6 months. Without the surgery she will die painlessly in the next few days. Most people, myself included, would pay for the operation, even if it meant that I couldn't afford to adopt a new puppy for a very long time after my old dog passed away.
I think it's telling that I'd feel obliged to do whatever I could to prolong my dog's life as long as I believed that her life would be, on balance, worth living. So, I would still want to get her the surgery, even if I knew that she would still have to live with a certain amount of pain in her last months. That would be excess pain that I would be inflicting on her, because the alternative would be a painless death. Yet, there's something about the continued existence of that individual that has intrinsic value.
However, now suppose the vet tells you that your elderly goldfish needs some very expensive therapy in order to prolong its life. Personally, I would much rather let nature take its course and buy a new goldfish instead of shelling out for some super-expensive fish ointment to keep the old goldfish going.
The difference in moral status between a dog and a goldfish is analogous to the difference between an octopus and a chicken. It's not just a question of whether I know the creature, or whether I have some custodial responsibility for it.
I probably haven't explained this very well. Maybe you guys can help me clarify my instincts about not eating "smart" animals.