If we were the only people left on earth, assuming that there isn't catastrophic damage to the earth or that we weren't being hunted down by zombies, aliens, etc., I suspect it would be surprisingly easy to survive. At first there would be an overabundance of virtually everything, such as medical supplies, food, fuel. And so most likely we could survive the first few years by living a nomadic lifestyle and moving from place to place scavenging for supplies. However, food eventually spoils, even boxed stuff, and so we would have to establish a farm of some sort and therefore eventually shift from a nomadic lifestyle to that of a farmer. An alternative to this is hunting and therefore a more tribe-like situation can be expected. At first we may have leaders to help organize and guide everyone, but as a norm is established in the day to day life I expect that we will become more democratic. I think the most important thing to remember is that usually disharmony amongst a group usually results from a lack of resources, limited space, etc. If everyone keeps a positive mental outlook and learns to efficiently use the abundant resources available to them I think that we would be able to survive pretty easily. And I know realize that I haven't answered a single one of your questions in the description box... Just going to slowly walk away...