Yes, we are taught that God put animals on Earth to be used according to our wishes. Singer claims on page 117 that "some" non-human animals may be considered persons when compared to people who are intellectually disabled or young children who have not developed into full adults. This is his idea that speciesism is wrong based on our belief that humans are at the top of the moral hierarchy. However, Singer goes on to say that it is very difficult to determine whether some animals are self-conscious or rational; however, in the case of humans beings it is readily apparent that most humans are self-conscious. I believe he said that one of the reasons that we should simply treat animals better is that because some animals do show signs of complex thought processes, such as other primates. He claims that these other primates are therefore close to being our equals because they can see themselves are existing in the future and planning an action to be carried out in the future.
Singer gives other reasons for not eating animals including that we have many other food sources and should simply use these other sources because killing animals implies they are but mere objects. So, according to Singer we should not eat most other animals, except maybe fish; however, I doubt that this will ever happen because in reality most people don't give equal consideration to pigs, cows, chickens, and all other farm animals. What makes Singer hard to put a finger on is that at the end of his chapter, he says "There is no single answer to the question: Is it normally wrong to take the life of an animal?. Is he saying that it depends on the animal in question? As to why we shouldn't eat people who have been euthanized, I would say this is because of the idea that eating another person is too great of a taboo to break. In our society we have generally accepted that a funeral and burial are part of the grieving process or in some cases cremation. However, if Singer were to examine this topic he may find it objectionable as well because of indirect utilitarian reasons he uses against killing. He speaks of the effects that the action will have on relatives and others around. Nonhuman-animals are not normally bothered if they see us eating a hamburger or a slice of bacon because they are not aware of what we are eating to begin with. If human beings were aware that we were eating each other, this would create a state of constant anxiety.