It is difficult to determine exactly how far Clarke intended the religious metaphor to go. Certainly, there are some logical flaws in the plot in these chapters. For instance, neither the Overlords nor the narrator attempt to rationally or logically explain what is happening to the children. In a novel where so many characters—particularly the Overlords—cherish science and reason, the transformation of the children is viewed as an almost mystical or magical event. Clarke has often been an advocate of the idea that any technology, sufficiently advanced, will seem like magic to someone who doesn't understand it—for instance, showing a television to a medieval person. But in the case of the Overmind, technology isn't an issue. The Overmind is, in theory, an alien creature, one who crosses the universe in an immaterial form, absorbing other races that evolve into its collective. The entire concept of the Overmind, and the children's transformation, is an idea that edges much closer to fantasy than science fiction. It may be why, in the paperback edition, Clarke added the comment, "The opinions expressed in this book are not those of the author." In Childhood's End, more than in any of his other works (including 2001: A Space Odyssey), Clarke strays from the pretensions to realism for which science fiction usually strives.
This sense of the fantastic is also supported by Karellen's speech. Karellen claims that, if humanity were to use science to discover the secrets of telepathy and extra-sensory perception, they would become a "telepathic cancer" that would cause great problems for all of the universe. There seems to be a number of questions here. First, both the Overlords and most humans in the novel are, like Clarke, great supporters of science, logic, and rationality. But Karellen is essentially telling humanity that the powers of the Overmind cannot be understood in scientific terms—despite Karellen's own admission that the Overlords are trying to decipher the secrets of the Overmind by studying it. Clarke turns his back on his belief that logic and empirical science can provide all the answers—giving Childhood's End a distinct spiritualistic overtone (which may be one of the reasons Clarke later said that the opinions"in the book were not his own). This appeal to mysticism and transcendental nirvana, which is a good description of the children's transformation into the Overmind, is unique among Clarke's books and may be part of the reason why Childhood's End has remained his most popular work. Imagining that there is a God-like force out there, such as the Overmind, just waiting for humanity to attain a level of mental sophistication so that humans can join with it, has all the appeal of believing in a benevolent God that will someday draw mankind into Heaven.
But when one considers the Overmind in a less spiritual and more rational context, the picture becomes more sinister. The Overmind is an alien force that absorbs races into its collective form, eliminating their individuality and destroying their planet in the process. Furthermore, there is apparently no alternative to the Overmind's tyranny, since even the Overlords, who can never join it, must forever do its bidding or be destroyed. One might wonder whether the Overlords might consider allowing a race such as humans to become this "telepathic cancer"—would they really be destructive or would they offer a new alternative, a challenge, to the tyranny of the Overmind? The Overlords have lied to humanity for over a century. It seems entirely fair to question Karellen's use of terms such as "telepathic cancer" and his unquestioned allegiance to the Overmind.