From a simple utilitarian perspective, identifiability is bias. By increasing altruism toward the identifiable victims, it may reduce altruism toward the unidentified ones, who are often the ones most in need of help. On the other hand, it could also increase overall altruism, by making people more willing to incur greater personal costs to help the identifiable victims.

So part of what I think is going on here is that giving to statistical charity is a slippery slope. There is no one number that it's consistent to give: if I give $10 to fight malaria, one could reasonably ask why I didn't give $100; if I give $100, why not $1000; and if $1000, why not every spare cent I make? Usually when we're on a slippery slope like this, we look for a Schelling point, but there are only two good Schelling points here: zero and every spare cent for the rest of your life. Since most people won't donate every spare cent, they stick to "zero". I first realized this when I thought about why I so liked Giving What We Can's philosophy of donating 10% of what you make; it's a powerful suggestion because it provides some number between 0 and 100 which you can reach and then feel good about yourself.

Then identifiable charity succeeds not just because it attaches a face to people, but also because it avoids the slippery slope. If we're told we need to donate to save "baby Jessica", it's very easy to donate exactly as much money as is necessary to help save baby Jessica and then stop. The same is true of natural disasters; if there's an earthquake in Haiti, that means we can donate money to Haiti today but not be under any consistency-related obligations to do so again until the next earthquake. If Haiti is just a horrible impoverished country, then there's no reason to donate now as opposed to any other time, and this is true for all possible "now"s.

Feedback appreciated as I've been planning to make a top-level post about this if I ever get time.