I agree, and think this is closest to reality the way I've observed it. I think most people want more and better things for themselves - this part I believe is a natural instinct present in the majority of human, probably a result of some evolutionary survival mechanism. However, I think people generally also have some limits on what they are willing to do to advantage themselves over others around them. The problem is that this limit varies greatly among individuals. Some people are not willing to take advantage of a fly for self-gain, while others are willing to take advantage of anyone and anything for self-gain. It's a complex problem that I think is difficult to solve in communities, especially in large, more loosely-knit ones (i.e., anything larger than a tribe or village).