an incorrigible liar—a blatant piece of projection of his own flaws onto another. He also condemns the whole East as distorted, pitting it in judgment against the snow, Christmas wreaths, and purity of his beloved Midwest.

Nick is a snob, at times, too, who judges Gatsby while also falling under his spell and taking his side. Nick judges Gatsby, for example, for his factual blunders, such as talking about big game hunting in Europe (which would only be done in Africa or India) and saying San Francisco is in the midwest.

Nick comments on honesty as his cardinal virtue. Fitzgerald cues us to see through that observation by placing it right after Nick has admitted he is lying to a girlfriend back home about their relationship. Nick might pretend, at times, to being nothing more than an observer, but he writes this story out of a deep sense of injustice and moral indignation (i.e. judgment). He writes it to defend Gatsby and to condemn the ultra-wealthy Buchanans for their abuse of privilege, wrecking lives and leaving others to clean up the mess.

In answering this question it's important to acknowledge the significance of Nick's relatively humble Midwestern background. He's been brought up in a completely different environment to those he encounters once he heads out East. Ordinarily, one can well believe that Nick isn't someone prone to judging people. In that sense, we can take his words at face value.

But in a way that's only because he's never met anyone quite like Gatsby or Tom Buchanan or Daisy before. These are all larger-than-life characters, who almost demand judgment on how they live their lives.

Initially, Nick tries his best simply to observe their lives. But he quickly realizes that this is impossible, that some degree of judgment is necessary to make sense of it all. To Nick, almost none of the things he witnesses can be properly understood without some kind of perspective. Such perspective, of its necessity, needs to be informed by subjective judgment.

Nick may not want to judge, but under the circumstances he has little choice in the matter; he can't simply observe from a distance the often outrageous actions of the other characters and jot down his findings as if he were an anthropologist studying a remote tribe.

Your question gets to the heart of the novel and the development of Fitzgerald's theme. The answer lies in the structure of the novel and its use of flashback. When the novel begins, Nick has returned from living in the East. He speaks to us as a man who has been through a profound experience and is still dealing with it.

He begins by telling us of his family background and how he grew up. He explains that as a result of his father's influence, he is "inclined to reserve all judgements [sic]." Then Nick moves on to this statement:

And, after boasting this way of my tolerance, I come to the admission that it has a limit. Conduct may be founded on the hard rock or the wet marshes but after a certain point I don't care what it's founded on.

This is an important passage, for it shows that despite his tolerant nature, Nick does not accept all behavior; at some point, he expects people to base their conduct on some kind of moral code. When he says "I don't care what it's founded on," the implied conclusion of that sentence is "so long as it is founded on something." Nick continues, saying that when he came home from the East, "I wanted the world to be in uniform and at a sort of moral attention forever."

Before Nick left home, he was basically nonjudgmental; by the time he returned, he had made strong judgments about the kind of human behavior he had witnessed there. Nick admires Gatsby for his naive romanticism and his absolute integrity in pursuing his dreams. He detests the Buchanans, judging them to be careless and irresponsible in their wealth and privilege, and amoral in their treatment of other people. According to Nick, the Buchanans were the "foul dust" that "floated in the wake of [Gatsby's] dreams." Nick's moral judgments are those of Fitzgerald. Through Nick, Fitzgerald condemned the social stratum in American society represented by Tom and Daisy.

He does judge those around him-just like every other human being. Remember, just because someone is narrating a story, doesn't mean their point of view is reliable. In fact, immediately after telling us of his ability to reserve judgment, he complains of being “privy to the secret griefs of wild, unknown men,” and making “riotous excursions with privileged glimpses into the human heart” against his will. In fact, he admits that “most of the confidences were unsought.” He even acknowledges when introducing Gatsby that “represented everything” for which Nick had “an unaffected scorn.” Thus, his moral values and prejudices are evident at the outset of the novel.

While he may be more open-minded than other characters in the novel (Tom, Daisy, and Jordan jump to mind), he isn't completely straightforward or honest (although he "suspects himself of one cardinal virtue"-honesty). See, for example, his first impressions of Meyer Wolfsheim, The Wilsons, and party-goers at Gatsby's. Each of these reveals some bias on his part.

Indeed, by the end of the novel he has judged each character for one misdeed or another. His final verdict of Tom, Daisy, and Jordan is that they "“smashed up things and creatures and then retreated back into their money or their vast carelessness, or whatever it was that kept them together, and let other people clean up the mess they had made.” While this is a valid observation, the negative connotation of "smashed", "carelessness", and "mess" reflect Nick's view of events.