"[6] Other activists who claim that their attitudes to animals changed after reading the book include Peter Tatchell[7] and Matt Ball.

In a lengthy debate in Slate, published in 2001, Richard Posner wrote, among other things, that Singer failed to see the "radicalism of the ethical vision that powers [his] view on animals, an ethical vision that finds greater value in a healthy pig than in a profoundly intellectually challenged child, that commands inflicting a lesser pain on a human being to avert a greater pain to a dog, and that, provided only that a chimpanzee has 1 percent of the mental ability of a normal human being, would require the sacrifice of the human being to save 101 chimpanzees."

Utilitarianism, Nussbaum argues, ignores adaptive preferences, elides the separateness of distinct persons, misidentifies valuable human/non-human emotions such as grief, and calculates according to "sum-rankings" rather than inviolable protection of intrinsic entitlements.

They derive their radical moral conclusions from a vacuous utilitarianism that counts the pain and pleasure of all living things as equally significant and that ignores just about everything that has been said in our philosophical tradition about the real distinction between persons and animals.

He writes of how he arrived in Oxford in October 1969, and in 1970 had lunch with a fellow graduate student, Richard Keshen, who avoided meat.

[13] A revised edition, titled Animal Liberation Now: The Definitive Classic Renewed, was released on 23 May 2023, featuring a new foreword by Yuval Noah Harari.