I think you will find that "The Red Queen" by Matt Ridley explains it pretty well, in terms of game theory. Of course the game theory stuff is just analogical and suggestive, but I find it convincing.
Basically the default condition (just because it's mathematically the simplest) is where everyone is looking out for himself. That's the imaginary "state of nature" that Thomas Hobbes depicted in "Leviathan":
"In such condition there is no place for industry, because the fruit thereof is uncertain, and consequently, not culture of the earth, no navigation, nor the use of commodities that may be imported by sea, no commodious building, no instruments of moving and removing such things as require much force, no knowledge of the face of the earth, no account of time, no arts, no letters, no society, and which is worst of all, continual fear and danger of violent death, and the life of man, solitary, poor, nasty, brutish, and short".
Writing in the 17th century, of course, Hobbes knew little about evolution and nothing of ethology. His knowledge of pre-agricultural societies was drawn exclusively from the travellers' tales of those who had been to the Americas, Africa, or the East Indies. Thus he assumed, reasonably enough, that without formal states and societies people would have no communities at all. That turns out not to be the case, as hunter-gatherers normally live in groups ranging from family size to a few hundred - and they cooperate intensively.
Models of Hobbes' extreme case show that, as he expected, it's not good. People do vastly better if they cooperate, so we almost always find society developing naturally. People develop morals, and come to expect honesty and straight dealing - even altruism, which is often repaid.
Now here is the interesting part: in a society where 19 out of 20 are honest, a tempting niche opens up for those who aren't. By pretending to be honest, these criminals (or banksters, politicians, marketing executives, lawyers or whatever you want to call them) leech off the work of others to live comfortably with little effort. It seems that mathematics and nature are against efforts to make everyone good, because in a society where most people are good it is just too tempting to be bad.