One might call the position set out in the quote 'insinuation by absurd association'. No one in their right mind believes in goblins, hobbits or truly everlasting gobstoppers. By putting 'God' in the same list the seed is sown that belief in God is just as absurd as belief in these other things. Whether the grounds for belief in the existence of God are reasonable - rationally justified - or not, they are epistemologically significant, worthy or serious argument - which the fact that Baggini has devoted a book to the topic confirms. This is not the case with the other items on Baggini's rhetorically contrived and bias-inducing list.
Baggini has done a lot of good work in making philosophy accessible but this passage is a dip in his achievement.
'Naturalism' in the quote refers to the 'belief that there is only the natural world and not any supernatural one' (Baggini, 4). This is Baggini's own view :
We are now in a position to look at what the evidence for
naturalism, and hence for atheism, is. The claim I would make is
that all the strong evidence points to the truth of atheism and only
weak evidence counts against it. This may seem like a strong claim
but I really do think it is justified (Baggini, 17).
The existence of God is to my mind a discussable matter. If Baggini had simply been outlining an atheist position in the goblin passage, without any commitment to it, the list would have been fine. But when, as the passage just quoted shows, it is his own position, he should not rhetorically have undermined the theistic position in advance by associating God with plainly, unarguably non-existent things.