In their 2012, 2014 and 2016 collaborations she and Singer set out to explain and defend act utilitarianism and suggest a resolution to what the late 19th century British philosopher Henry Sidgwick called “the profoundest problem of ethics", the apparent rationality of both ethical egoism and utilitarianism.

Oxford philosopher Derek Parfit (1942–2017) expressed the view that their argument against the rationality of egoism carried "some force" though, as Lazari-Radek and Singer themselves acknowledge, it is not "decisive".

[3] In his review[4] of Lazari-Radek and Singer's book, The Point of View of the Universe: Sidgwick and Contemporary Ethics (2014), philosopher Bart Schultz, director of the Civic Knowledge Project at the University of Chicago, describes de Lazari-Radek as “a rising star … of philosophical utilitarianism", stating that their “book might well represent the most significant statement and defense of act utilitarianism since the 19th century, when the classical utilitarianism of Bentham, Mill, and Sidgwick were the spirit of the age."

[3] In July 2017 her and Singer's second book was published Utilitarianism: A Very Short Introduction, of which Jeff McMahan, White's Professor of Moral Philosophy, Oxford University, has said: "Written with characteristic clarity by the acknowledged heirs of the founders of utilitarianism, this discussion is authoritative, sympathetic though not uncritical, and remarkably comprehensive - in a word, ideal.

She persuaded Singer to embrace hedonism instead of preference utilitarianism during their collaboration on The Point of View of the Universe.