There is nothing new to see here. This is yet another non-expert (a newscaster), who had yet another life of subjective suffering (a mother unable to answer his questions about God correctly, and a father that was killed in war), who is offended by the idea that sin, especially sexual sin (of which he had in plenty, with homosexual liaisons as a young man), is bad and that God will judge him, telling us that arguments for the existence of God are "futile" because God is entirely a creature of our imaginations, and we need to get over it. And he makes much about there now being 50,000 Humanists in Norway, with "hopes" for 100,000 by this year -- in a country of 4 1/2 million. This despite the immense growth of Christianity in the Third World.
From making much over Europe's near-empty churches and uneducated clergy to criticizing Matthew for a "mistranslation" of Is. 7:14; from objecting to the Dark Ages (no longer called that by serious historians) and indulgences to assuming the JEDP theory true just because a liberal said so; from following the standard view about anonymity of the Gospels to hinting that Jesus was homosexual and/or self-delusional; All in the Mind is little more than a catalog of the most common skeptical arguments molded into declarative assertions. Kennedy offers not a single original argument here; even his merely historical portions of the book, consisting of a very, very brief and simplistic look at the evolution of religious thought and the growth of atheism, are done far better, and in a far more interesting and complete way, in a variety of sources.
Kennedy thinks we're all deluded for believing in any God, especially the Biblical one. That estimation, coming as it does from someone who clearly used no more sources than he was able to find at the closest library, calls for no serious consideration. Since there is nothing within that has not already been refuted on this page and elsewhere, the reader is free to give it a pass.