The New Atheists (Dawkins, Hitchens, Dennet, Harris, et al) are working out the metaphysic of a liberal democracy that is considered “absolute”. That is, if you consider liberal, individualistic, democratic society to be the best (or only) way to live, that belief needs a certain theory to back it up. The NA’s have done a certain amount of thinking on this score and have worked their way back to the presuppositions that are implied by modern, liberal, democratic society.
For Christians, ideas like “modern political freedom” are not and cannot be absolute. (Really, for any human being they can’t be absolute, but most people in Western society haven’t picked up on this fact yet.) We recognize that our current political and social freedom is contingent on the common acceptance of certain, basic, society-wide values and norms - specifically, Christian ones. Given society-wide acceptance of those values and norms, there can be quite a lot of freedom for individuals to choose ways of worship, certain moral values, etc, without threatening the structured peace of society. It’s perfectly fine, then, from a political point of view, to have atheists in your society and allow them to not go to church, but only as long as they’re Christian atheists.
If, however, you take modern political and social freedom as an absolute, then there cannot be a Higher Being who has created us and determines what is right and wrong for us to do, personally and socially. The NA’s recognize that if there is a God who has created, then what he says goes. But what he says can’t go (or else modern liberal democracy isn’t absolute). Therefore, there is no God. If A then B. Not B, therefore not A.
Richard Dawkins especially is fascinating because his main argument is almost entirely a moral one. The “science” is just a smoke screen. (Not that I think for a second he isn’t convinced that Science disproves God.) But Dawkins basically says, “Religion disables a community from considering modern democratic political and social freedom from being an absolute. But they are absolute. Therefore, religion is bad.”