Good article in the Wired Science blog: The More Victims, the Less Severe the Judgment. It's about a study of jury verdicts that found, "the more victims are involved in a case, the less harshly the perpetrator of the crime is penalized."
It's called "identifiable victim bias," and it explains why someone who murders one or two people tends to be much more harshly punished than someone who causes the deaths of hundreds or thousands.
The study, titled "The Scope-Severity Paradox: Why Doing More Harm Is Judged to Be Less Harmful," is available here (PDF). A key point:
People empathize with people by putting themselves in the other person’s shoes. The more shoes there are, the harder it is to empathize with any single individual. People don’t multiply their feelings of empathy by the number of people involved.
This is important for fundraisers, not just defense attorneys.
We get people to care about something not by emphasizing how huge the problem is -- but by making it seem small, graspable, and solvable.
We're fighting some incredibly huge problems. But we're always going to have trouble getting people to stand with us with their donations if we just talk about the size of the problem.
So next time you find yourself trying to gin up emotion about the size of the problem you want donors to help you solve, stop. Find an "identifiable victim." Things will go better.