Was sitting at the bar last night, reading IDBIA and trying to summarize the main points. This is just assuming Hedges has already put forward his points and the rest of the book (I'm more than halfway) is just more supporting evidence.
The major assumption Hedges starts off with is that human nature is flawed. Whether you call it sin, or something else, human beings are constantly afflicted by greed, for wealth and power, and temperment for violence. This is something that has been shown throughout the history of human civilization, cycles of wars and unrest. Hedges sees in this no moral advancement of humanity; we are still stuck with the same basic flaws we started with, and while individually we can work out this sin (or whatever you want to call it) through ethics, and tempering of our flawed nature, while collectively we are brutal and violent. Utopia, is by Hedges, impossible.
Now, generally, people can individually or at a collective level develop systems of ethics (either religious or nonreligious) that work in tempering human nature. Athiests and theists alike can do this, it doesn't require a believe in a personal god to be moral. All these ethical systems are still working on the basic concept that human nature is flawed, it has always been flawed and it will always be flawed, so we make "rules" for ourselves and others to temper these flaws.
However, if you go beyond that, and find believe in some sort of moral progress of humanity, and have a vision of a future utopia, then you have forsaken this idea of a flawed humanity. You see this utopian vision and the "ends justify the means". Whether this vision is of a unified people under science and technology or a glorious heaven, they are both false visions because they fail to accept the reality of human nature. This is something that both christians who believe in the rapture and visions of the second coming and athiests who see a technological utopia where all the wrongs of human society will be banished share. They are fundamentalists, in the sense that they hold to a fundamental vision that does not match reality and cannot be swayed from this vision. This fundamentalism leads to self-deification and the inability to do no wrong in their quest.
In shorter summary, human nature is flawed. Ethics can be used to check these flaws. Utopia is impossible, and those who have utopic visions are dangerous in that they have lost sight of flawed humanity, allowing them to justify any act in their efforts to make this vision a reality. Fundamentalists, either Theist or Atheist, are bad.
