They had a point. The answer to this was as follows: "Medical, biologic and natural science has long since proven that this is a living human from conception. Our founding fathers, in the charter of this republic spoke clearly, stating "we hold these truths to be self evident, that all men are created equal and that they are endowed by their Creator with certain unalienable rights — of life, liberty and the pursuit of happiness." The pro-life response accordingly, was very direct. "Religious belief is a powerful motivator for the individual person. But this is not merely a religious issue, it is primarily a human rights issue, a civil rights issue, and our nation and other western nations, make laws to protect civil and human rights."
However, when co-authoring The Point of View of the Universe (2014), Singer shifted to the position that objective moral values do exist, and defends the 19th Century utilitarian philosopher Henry Sidgwick's view that objective morality can be derived from fundamental moral axioms that are knowable by reason. Additionally, he endorses Derek Parfit's view that there are object-given reasons for action.  Furthermore, Singer and de Lazari-Radek (the co-author of the book) argue that evolutionary debunking arguments can be used to demonstrate that it is more rational to take the impartial standpoint of "the point of view of the universe", as opposed to egoism—pursuing one's own self-interest—because the existence of egoism is more likely to be the product of evolution by natural selection, rather than because it is correct, whereas taking an impartial standpoint and equally considering the interests of all sentient beings is in conflict with what we would expect from natural selection, meaning that it is more likely that impartiality in ethics is the correct stance to pursue.