Also, even if we ignore pragmatism, morally speaking the Singer metaphor is failed because the proposed scenario (child drowning, child starving) does not model realistically the problems of the world.
The world has very few cases of competent people under immediate threats, and many cases of incompetent people causing misery. 
By using an extreme example, he threw away all the nuance, and the understanding of what true suffering mitigation has to be. (Mass Colonization)