We scientists have way too much a tendency to simplify problems. I guess it actually comes to us naturally. Take the simplest unit, separate out all the confusing, external factors. Study it. Make sure you understand it. And in psychology that means the person studying the individual. But if you want to study our social nature, if you want to study processes that will lead to war and peace, you don't learn all that much by looking at the single individual. A lot of the important things are emergent facts about us, things that you can only see when you get a lot of us interacting.