The day may come, when the rest of the animal creation may acquire those rights which never could have been withholden from them but by the hand of tyranny. The French have already discovered that the blackness of the skin is no reason why a human being should be abandoned without redress to the caprice of a tormentor. It may come one day to be recognized, that the number of the legs, the villosity of the skin, or the termination of the os sacrum, are reasons equally insufficient for abandoning a sensitive being to the same fate. What else is it that should trace the insuperable line? Is it the faculty of reason, or, perhaps, the faculty of discourse? But a full-grown horse or dog, is beyond comparison a more rational, as well as a more conversible animal, than an infant of a day, or a week, or even a month, old. But suppose the case were otherwise, what would it avail? The question is not, Can they reason? Can they talk? But, Can they suffer?---Jeremy Bentham
Nearly all the external signs that lead us to infer pain in other humans can be seen in other species, especially the species most closely related to us—the species of mammals and birds. The behavioral signs include writhing, facial contortions, moaning, yelping or other forms of calling, attempts to avoid the source of pain, appearance of fear at the prospect of its repetition, and so on. In addition, we know that these animals have nervous systems very like ours, which respond physiologically as ours do when the animal is in circumstances in which we would feel pain….
…[T]here is one other thing we can that is of supreme importance; it underpins, makes consistent, and gives meaning to all our activities on behalf of animals. This one thing is that we take responsibility for our own lives, and make them as free of cruelty as we can. The first step is that we cease to eat animals. Many people who are opposed to cruelty to animals draw the line at becoming vegetarian. It was of such people that Oliver Goldsmith, the eighteenth century humanitarian essayist, wrote: ‘They pity, and they eat the objects of their compassion.’
Indeed, the food wasted by animal production in the affluent nations would be sufficient if properly distributed, to end both hunger and malnutrition throughout the world.
Anyone writing on the topic of the treatment of animals must acknowledge an enormous debt to [Peter] Singer. The growing public awareness of the gruesome details of factory farming is in no small measure due to the wide readership his work, especially Animal Liberation [1st ed., 1975], has rightfully commanded. [….] But this debt to Singer’s work does not imply that his moral argument for vegetarianism is adequate.
Vegetarianism is not supererogatory; it is obligatory.
[Tom Regan’s] The Case for Animal Rights  is perhaps the most systematic and explicitly worked out book in animal ethics.
The expression ‘animal rights,’ while often used loosely as a synonym for animal liberation, properly has a more limited application, since not all liberationists agree that focusing on the concept of rights is particularly useful, and some even deny that animals (or humans) possess moral rights—Peter Singer being a prominent example.
The animal liberation movement, as a broad set of philosophical, political, and cultural activities united by a rejection of the idea that animals are essentially resources, is to be distinguished from the traditional animal welfare movement, which has sought to minimize the suffering of exploited animals but has not fundamentally challenged the view that animals are essentially resources.
Ahimsa, the doctrine of non-injury to all living beings, is a prominent part of Hinduism, Buddhism and Jainism. [….] The influence of Buddhists and Jains in India has been instrumental in limiting the formerly widespread practice of animal sacrifice. Buddhism and Jainism both stress the interrelatedness of all forms of life. Vegetarianism is an ideal for both. All creatures, it is said, even the simplest, love life and seek protection from harm.
Pythagoras has been called the first animal-rights philosopher. He advocated vegetarianism, and he and his followers rejected the use of animals in religious sacrifice.
Of the major ethical theories, contractarianism has been least hospitable to the notion of animal liberation.
When someone is behaving in a particularly anti-social manner, we speak of the person acting ‘like an animal’ or being ‘brutish.’ Yet human beings outdo all other creatures in terms of cruelty and unnecessary aggression against members of their own and other species. Can it be that in attributing ‘beastly’ behaviour to non-human animals we are projecting the dark side of our own natures onto convenient scapegoats?
Many people find themselves sharing meals with moral vegetarians, perhaps for the first time having to acknowledge in some way or the other that using animals for food at least stands in need of justification. To some degree what happens in laboratories and slaughterhouses has been brought to light. Those who retain ‘Old Macdonald’ fantasies of how farm animals are treated now border on denial or culpable ignorance. Behavior change lags this growth in awareness and various contradictions in our treatment of animals are painfully obvious. But even the recognition of contradiction is itself a sign of moral progress, at least compared to the moral complacency that governed our treatment of animals prior to the 1970s. While widespread legal reforms have yet to occur in the United States, the European Union is in the process of transforming the conditions under which hundreds of millions of farm animals live.
[I]t is not clear that restricting the use of animals in science would result in less freedom of inquiry. In fact, by directing resources away from entrenched institutions and calcified research programmes, such restrictions could well contribute to greater effective freedom of inquiry for really creative scientists with new and exciting ideas. [….] It would require considerable argument and evidence to show that restricting animal research really would result in diminished freedom of inquiry. In the absence of such argument and evidence, we should resist the temptation to make the all-too-ready inference that restrictions on the use of animals would constitute restrictions on freedom of inquiry. Still less should we conclude that such restrictions would impede the growth of knowledge. Even if restrictions on animal experimentation constituted restrictions on freedom of inquiry, it does not follow that it would be wrong to initiate such restrictions. Freedom of inquiry is not an absolute value. We accept and even demand some restrictions on freedom of inquiry, even when this stands in the way of obtaining valuable knowledge. We do not allow research on unconsenting prisoners, unwanted children, or unloved old people. We find the research conducted by Nazi doctors in concentration camps utterly repugnant, however valuable the information obtained might be.
…[T]here is a moral presumption against keeping wild animals in captivity.
…[T]here is little evidence that zoos are very successful in educating people about animals. [….] Because what zoos [do in fact] teach us is false and dangerous, both humans and animals will be better off when they are abolished.
Nonhuman animals are capable of dignified existence…. Dignified existence would seem at least to include the following: adequate opportunities for nutrition and physical activity; freedom from pain, squalor, and cruelty; freedom to act in ways that are characteristic of the species…; freedom from fear and opportunities for rewarding interactions with other creatures of the same species, and of different species; a chance to enjoy the light and air in tranquility. The fact that humans act in ways that deny animals a dignified existence appears to be an issue of justice, and an urgent one.
---Martha C. Nussbaum
[T]hrough their daily behavior, people who love [their] pets, and greatly care about their welfare, help ensure short and painful lives for millions, even billions of animals that cannot easily be distinguished from dogs and cats.
---Cass R. Sunstein
[O]ur moral schizophrenia is related to the status of animals as property, which means that animals are nothing more than things despite the many laws that supposedly protect them. If we are going to make good on our claim to take animal interests seriously, then we have no choice but to accord animals one right: the right not to be treated as our property.
---Gary L. Francione
In the case of farmed animals, federal law is essentially irrelevant. The Animal Welfare Act, which is the primary piece of federal legislation relating to animal protection and which sets certain basic standards for their care, simply exempts farmed animals, thereby making something of a mockery of its title. No other federal law applies to the raising of farmed animals, and, consequently, the U.S. Department of Agriculture has no statutory authority to promulgate regulations relating to the welfare of farmed animals on farms. As a result, the Humane Slaughter Act is the primary federal legislations affecting farmed animals. It requires that livestock slaughter ‘be carried out only by humane methods’ to prevent ‘needless suffering.’ Astoundingly, regulations promulgated pursuant to the statute exempt poultry, the result of which is that over 95 percent of all farmed animals (approximately 8.5 billion slaughtered per year) have no federal legal protection from inhumane slaughter. Even given its limited applicability, the Humane Slaughter Act would constitute a significant imposition on industry except for the fact that there are no fines available for violation of the statute and significant penalties are never imposed. There can be little doubt that the act is not being effectively enforced.
---David J. Wolfson and Mariann Sullivan
State anticruelty statutes are criminal statutes that apply generally to all animals and not simply farmed animals. Thus, they are usually worded in very broad and largely undefined terms, and do not specifically require affirmative acts, such as adequate exercise, space, light, ventilation, and clean living conditions and, where they do specify affirmative requirements, do not explain, in detail, what those requirements are. For many reasons, there are substantial problems inherent in the governance of an industry’s conduct by means of a very general criminal statute, rather than a regulatory statute.
---David J. Wolfson and Mariann Sullivan
Of course people disagree about how people should treat animals. But the tension between competing beliefs is less remarkable than the tension between widespread practices and widespread moral commitments. Every day of every year, people engage in practices that ensure extraordinary suffering for animals. We believe that if those practices were highly visible, they would change, because many people already believe that they are morally unacceptable. This point makes existing treatment of animals extremely unusual. A great deal of progress could be made, not by challenging existing moral judgments, but by ensuring that they are actually respected.
---Jeff Leslie and Cass R. Sunstein
In short, consumers should be informed of the treatment of animals used for food, so that they can make knowledgeable choices about what food to buy. Disclosure of animal treatment would have the virtue of making markets work better; it would also have the advantage of ensuring more and better in the way of democratic discussion about the treatment of animals. Moreover, it would be possible to accomplish both of these goals without taking a stand on the issues that most sharply divide people. We might…obtain an agreement on a relevant practice—one of disclosure—amidst uncertainty or disagreement about the most fundamental issues, and protect animals from serious suffering in the process.
---Jeff Leslie and Cass R. Sunstein