Philosophy in the 1970s was coming out of a period dominated by ordinary language philosophy in which leading philosophers like A.J. Ayer argued that philosophy has nothing to say about what is right or wrong and should leave ethical questions to politicians and preachers.

Steven Pinker wrote in Better Angels of Nature that when he was a graduate student in psychology, he conducted what he describes as one of the worst things he's ever done—torturing a rat to death—but claimed that the difference between the 1960s and present time is 'like the difference between night and day,' though this claim appears to be false based on current animal research practices.

The major factory farming methods raise animals in locked huge sheds containing thousands or even tens of thousands of animals (particularly chickens), maximizing production efficiency at the cost of giving them no semblance of normal life, in order to keep flesh prices low.

Singer's Animal Liberation was well-received by philosophers in the 1970s, with most who engaged with it saying that philosophy should return to addressing important ethical questions, partly because other philosophers were already discussing Vietnam, civil disobedience, and civil rights.

The term 'speciesism' was not invented by Singer but was found in a leaflet published in the early 1970s by Richard Ryder, and when Singer encountered it, it provided a conceptual framework parallel to racism and sexism for understanding unjustified discrimination based on species membership.

The slippery slope argument against euthanasia was widely used in Netherlands debates in the 1980s when voluntary medical assistance in dying began, with opponents predicting it would lead to killing people regarded as useless, intellectually disabled, or politically undesirable, though this argument seemed to have weight because the practice was unfamiliar at the time.

Derek Parfit's philosophy of population ethics addresses the difficult question of whether bringing more beings into existence if they will lead good lives is actually a good thing, and whether this compensates for depriving an existing being of their life.

The key difference between justified and unjustified discrimination is not the characteristics of the discriminated group but whether the discriminating group's interests actually override the other group's interests; being of one race, sex, or species does not provide such moral override, but capacity for suffering does.

There are small numbers of farms that do treat animals well, give them good lives, and kill them without suffering, and if an animal that has lived a net positive life is killed humanely, purchasing products from such farms may not be ethically harmful because the animal would not have existed at all if not for the market demand.

Parkinson's disease affects millions worldwide and is a terrible, slow-acting condition; research to alleviate its symptoms could be defended if there were really no other way to find the treatment, as an example of animal research that might be justifiable.

Speciesism operates through the same mechanism as racism and sexism: a dominant group uses technological or other advantages to subjugate another group, then develops an ideology to justify that subjugation, as when Europeans used technology to enslave Africans and developed ideologies of racial superiority, or when male-dominated societies denied women property rights and voting rights.

Insects likely cannot suffer at all or suffer far less than larger animals with vastly more neurons, and therefore the moral concern for insect suffering is minimal or zero, though we cannot be entirely certain about insect sentience.

An anencephalic infant (born with only a brain stem, no cerebrum, destined never to be conscious) has less moral significance than a dog, cow, or pig because those animals can experience things and have good or bad lives from their perspective, whereas the anencephalic infant will never have conscious experiences.

Animal research ethics committees (institutional animal care and use committees in the United States) were introduced as a result of pressure from animal advocates, and Singer expected them to improve animal research standards more than they actually have.

Learned helplessness experiments in dogs involved training dogs to escape electric shock, then placing barriers to prevent escape, causing dogs to stop attempting escape after repeated shocks and passively accept the shock, with experimenters interpreting this as a model of depression in humans.

PETA (People for the Ethical Treatment of Animals) tends to focus on experiments that are not curing children's cancers as a matter of effective activism tactics, focusing on less defensible cases rather than the hardest cases, but this tactic creates pressure to maintain a strict party line against all animal experimentation even including potentially justifiable medical research.

Animal model research for PTSD is unlikely to be effective because humans have different awareness of what is happening, discuss trauma with others as a social process, and experience humiliation from abuse in ways that rats likely do not.

Stephen Suomi, a student of Harry Harlow, continued maternal deprivation research and received large grants from the National Institutes of Health until PETA opposition and advocacy led to the experiments stopping around 2015.

The scale of animal suffering from food production is vastly greater than any historical human suffering because we kill approximately 200 billion vertebrate animals annually for food, compared to 8 billion humans on the planet, and inflict miserable lives on them in factory farming systems.

The learned helplessness model has been abandoned for depression because experimenters themselves came to accept that it was not a good model for depression and that the label 'learned helplessness' was even wrong—the behavior was more biologically innate than learned—but researchers subsequently proposed using it as a model for post-traumatic stress disorder (PTSD).