I have a theory that human beings just don't scale up linearly. Less mathematically, I mean that just because 2 people work well together and 4 people might be more productive or complimentary to one another, I don't think that makes 400 humans or 4 million that much better and in fact beyond a certain limit it makes us worse at working together. I think there is an optimal size for most any human community or society and that size is governed by many things. Perhaps by the environment, the demeanor of the specific population, the stresses on that population and the resources available to it. One thing is for sure, I think that societies beyond a certain size bring out what is most horrible in humans and I think it all centers on the evolution of anonymity in a community and the loss of the perception of personal responsibility to the other members of that community.
I see this in my field of work, Emergency Medicine. I see people willing to step on others to get what they want despite the obvious pain someone else is in at the moment. I see the ramifications of other's choices that led to the death or damage of another simply so that they can satisfy their base instincts. They have no concept of the other person anymore.  I have worked in small towns with small ER's and large cities with level 1 trauma centers. I have lived in some of the largest cities in the US and on small islands and on the tops of mountains. No community is ideal, but some communities seem to work better than others, some are more sustainable and at the very least some at least limit the amount of ugliness any one member can express. There are still petty disagreements in small communities, dishonesty, ignorance... but in small communities every member has an identity and with that a responsibility to their own legacy. There is a loss of privacy but in the extreme I think it is the anonymity of privacy that allows people to let some of their baser instincts to control them. It becomes a snowball and before you know it, people follow their own impulses despite the negative impacts they often have on others because they know that their actions are not being associated with them personally. I am not sure this is intentional or even realized at the time but I think it is real. I have never seen the sort of horror in small communities that I see people inflicting upon one another in large cities. 

This is a rather unfinished thought, because I truly feel that this ties into another topic that is somehow involved - the loss of family communities and the longer term impact that is having on our society. Not that families in the past were perfect, far from it, but they still offered a few lessons and binders that seem to have been lost in our society. Things such as learning to deal with your conflicts and problems, being forced to .Being responsible to others in the family or at least being very aware of the impact your choices were making on those around you. If you made a decision and it hurt someone else, you knew about it and you had to either live with that repercussion or change your decision. With the loss of family I think the first brick was set for the loss of responsibility to our larger community. We became anonymous within our own small group when we lost our brothers, sister, parents. We made choices based solely on survival, what we needed or wanted. This has translated into our politics and communities as many of us have grown to become the leaders of the larger communities we have found ourselves in. 

I think that even without the family part, it is clear that once a society grows beyond a certain limit and individuals lose their identity within the community they also realize that they lose the responsibility to the others within it. Their choices slowly reflect more and more their focus on their wants and needs because they are oblivious to the wants and needs of those around them. Not out of greed or evil intent necessarily, but simply out of separation and lack of awareness. Slowly people decide that their interests are the only that exist and are the most important or they feel a sense of anger when they see other anonymous members of the society making choices that marginalize them for some other person's benefit. This triggers jealousy, vengeance, etc.... a whole host of human ugliness and a race to collect more for yourself and less for others.

Again, this was just an attempt to get some more feedback and thoughts on something that has been forming in my mind. Way off base? Other thoughts? I rarely have time to respond or read through this group at this time but I hope this generates some conversation. I will chime in as I can!