In appropriate circumstances we are justified in using humans to achieve goals (or the goal of assisting animals).
Peter SingerCheats prosper until there are enough who bear grudges against them to make sure they do not prosper.
Peter SingerWe should give the same respect to the lives of animals as we do to the lives of humans.
Peter Singer...chimpanzees, bonobos, gorillas, and orangutans are thinking, self-aware beings, capable of planning ahead, who form lasting social bonds with others and have a rich social and emotional life. The great apes are therefore an ideal case for showing the arbitrariness of the species boundary. If we think that all human beings, irrespective of age or mental capacity, have some basic rights, how can we deny that the great apes, who surpass some humans in their capacities, also have these rights?
Peter SingerAs for cages themselves, an ordinary citizen who kept dogs in similar conditions for their entire lives would risk prosecution for cruelty. A pig producer who keeps an animal of comparable intelligence in this manner, however, is more likely to be rewarded with a tax concession or, in some countries, a direct government subsidy.
Peter Singer