Arguably, "biased" is not the correct word to use in this powerful dystopian story. Rather, as the modern-day reader understands as the story progresses, John is a narrator that is rendered unreliable by his lack of knowledge and understanding of the world which he inhabits and its history. John is a narrator who has been brought up in a time set after the destruction of civilisation as we know it, and where a lot of the knowledge that is so integral to our lives today has been lost. Consider the following quote, which comes after John has crossed the river and entered the greatest "Dead Place" of them all:
It is not true either, what some of our priests say, that it is an island covered with fogs and enchantments. It is not. It is a great Dead Place--greater than any Dead Place we know. Everywhere in it there are god-roads, though most are cracked and broken. Everywhere there are the ruins of the high towers of the Gods.
The modern-day reader understands that this "Dead Place," from other hints given in the story, is actually the ruins of New York, that the "God-Roads" are highways and the "Gods" are actually humans who have brought down destruction upon themselves in the "Great Burning" through their scientific advances. The word "bias" implies a lack of self-knowledge or a deliberate promotion of one particular angle of an argument. John is definitely lacking in knowledge, but arguably this is not self-knowledge, and therefore it is more accurate to talk of him as an unreliable narrator, made unreliable by his separation from civilisation through time. This of course only serves to reinforce the author's warning: unless humans are able to use the knowledge they have gained responsibly, they will bring destruction upon themselves.