What's the harm in saying "there are starving kids in Africa" to get your child to eat his veggies?

You know this saying since it’s pretty much a parenting cliché used to cajole children to eat their vegetables: “There are starving children in Africa. You should be grateful that you have this food to eat.” I have never understood the logic that leads people to believe that mentioning such tragic information could motivate anyone to eat, let alone to develop a sudden appreciation for asparagus or rhubarb. If there are hungry children then there is a serious situation that should be fixed, right? How could begrudgingly eating the last bites alleviate trouble of that magnitude?

Mother and community psychologist, Tamara Brennan of Mexico explains on API's blog what she heard, as a 3 year old, when told to eat her vegetables and be grateful because there are starving children in Africa.