... when Baby Jessica fell to the well & she really suffered and her parents must have been incredibly miserable, she got more CNN coverage than Rwanda and Darfur, right? And the question is, why does this happen and why do people care so much? And it turns out, there's research on what's called the "identifiable victim effect."

  ... you would expect it as more lives are at stake, we would care more, maybe in a linear relationship. Or, maybe we would care more in the beginning & there'll be kind of a diminishing return ... But it turns out, the function is different: We care a lot about individual life and care less and less as the pie... as the number of people become bigger. 

  ... Stalin said, "One death is a tragedy, a million deaths is a statistic." And Mother Theresa said in the same spirit, "If I look at the masses, I will never act; if I look at the one, I will." ... It turns out that every time you activate cognition, calculation, thoughtfulness, you turn off the emotion — people care less and give much less. 

Dan Ariely (who unironically isn't moved by plight of the Palestinians) also discusses this in the introduction of his book, The Upside of Irrationality.