multifoliaterose:

[Following Singer's kid-in-a-pond parable: ] Most people value the well-being of human strangers. This is at least in part a terminal value, not an instrumental value. So why don't people give more money away with a view toward maximizing positive social impact?

That's not a precise way of putting it. There is a huge difference in how people view strangers that happen to be physically close at the moment, especially if they are perceived to belong to the same community in some sense, versus distant strangers that are out of sight.

You are expected to exert a reasonable effort to help strangers in dire trouble that you encounter physically. This includes, say, giving directions to someone who is lost, calling 911 if you find someone lying wounded, or pulling a drowning kid out of a pond. This social norm is, to my knowledge, a human universal. Its overall effects are positive by all reasonable standards, and it is entirely rational to suspect people who break it of serious personality defects. Life is immensely safer and more pleasant for everyone if you can expect random people around you to watch your back and care about you to some reasonable degree.

In contrast, people as a rule don't care at all about distant, out of sight strangers. Yes, they will often donate to charity in the name of helping them, but the reasons for such donations have little or nothing to do with the actual psychological mechanisms of care for fellow humans. Moreover, while attempts to help immediately present strangers almost always actually help them, the case for remote charity is much more moot. The law of unintended consequences is harsh and merciless whenever large-scale interventions in human affairs are undertaken, and it's illusory to believe that it can be avoided by some simple precautions such as those advocated by GiveWell. Whether or not people like James Shikwati are exaggerating their case, it is even more foolish and dishonest to dismiss them out of hand.

So, on the whole, when it comes to helping strangers, I readily admit that I feel a strong obligation to help strangers in cases of the first kind, and expect the same from others, while I'm largely indifferent and skeptical towards aid to distant foreigners. This is simply what human beings are like, and denying it is empty posturing -- there is practically no one who actually considers his obligations towards all strangers the same, or vice versa, no matter what the distance. When Singer conflates these cases, it is merely a reflection of his spherical-cow utilitarianism that has nothing at all to do with the real human moral instincts -- or any other actual aspect of humanity, for that matter. He is just proselytizing his own eccentric quasi-religious belief system.