The logic of moral interests seems to have a very weak hold when persons are asked to abandon their own utility preferences for cognitively less developed life forms. Our moral world is seldom presented to us as a utility calculation. In fact it sometimes seems downright immoral to calculate the costs and benefits of an ethical deed. We are expected to do what is right despite personal costs. This is how most people live ethically.
Ethics is the study of values and worth.
Philosophers like Mr. Singer are given the leisure to ponder these questions. They may often come up with what appears to be ludicrous conclusions. Their conclusions deserve a respectful hearing. If their conclusions are truly outlandish, they will be rejected, as individuals act upon what they value. Utilitarianism cannot be scripturally sound because it emerges from the preferences of life forms with interests and not in the far reaches of the mystical beyond.