If people know that their children aren't likely to die in infancy, they are more likely to voluntarily limit the size of their families, for any number of reasons, most of them good. That's what the Gateses are trying to do. I like the idea of a couple having 2 children they plan on sending to college, better than the idea of a couple having 12 children in the hopes that 5 of those children will live long enough to become day laborers, don't you?