I am always looking for the theology behind things. For McGrath, it is hard to find. The closest is probably pages 175-178, where he recounts his testimony of being an atheist before becoming a Christian:
"By 'atheist', I mean precisely what the word has always been understood to mean - a principled and informed decision to reject belief in God." (p 175, emphasis in original)This is worrisome. Where is sin and repentance?
"I began to realize how little I knew about the history and philosophy of the natural sciences, or the nature of Christian belief... To cut a long story short, I discovered that I had rejected what I did not really understand... I began to discover a dimension to life that I had hitherto suppressed." (p178)
Also, McGrath seems to favor the atheist definition of faith (although it is conditional, he doesn't expand):
"If 'faith' is defined as 'belief lying beyond proof'" (p 180)
That said, McGrath does shed some light on why outward atheism had such a strong presence in Europe, but remained a minority in America. Atheism, as formulated in Europe, is a static attack on the Christianity of Europe - the mixture of Church and State. State Churches where leadership is a political appointment, and where Christianity is associated with nationalism and "the old way".
By rebelling against old, corrupt, and inadequate ways - and offering a new "global membership" (to eliminate nationalism) - atheism attracted many people who were oppressed under the old ways. Rebellion against kings and entrenched power became rebellion against the Church and, ultimately God. Where "Christendom" had been an instrument of oppression, atheism offered freedom.
In America, there was (and is) no tie between Church and State. Indeed, the local churches were often reactions against State Churches from Europe. When rebellion came, the churches were fully integrated into the spirit of rebellion.
This is why McGrath sees atheism in its twilight. The State Churches of Europe have been broken for more than a generation. The atheism of the last generation is no longer relevant for today. It cannot stand on its own, it is totally reactionary.