We see Nick becoming increasingly judgemental throughout the novel. By the end he sees the people he has been associating with in the East as morally bankrupt and he returns to the Midwest so as not to be exposed to their superficial ways.
Nick ultimately accepts that his moral values are conservative, mid-Western ones. He begins the book by saying that he abides by his father's dictum in withholding criticism if he is not in full possession of the facts, and he is therefore "inclined to reserve all judgements". But he goes on to say that his tolerance "has a limit".
However, there remains a certain confusion and ambiguity to Nick's moral code. At one point in chapter eight, he simultaneously expresses disapproval of Gatsby and says something kind to him:
'They're a rotten crowd,' I shouted across the lawn. 'You're worth the whole damn bunch put together.' I've always been glad I said that. It was the only compliment I ever gave him, because I disapproved of him from beginning to end.
Another example of the paradox of Gatsby (in Nick's eyes) is that his lifestyle was funded by "corruption" but his dream was "incorruptible".
Although Gatsby does have a biological father in Henry Gatz, Gatsby is a created persona and so he doesn't really have a father. Or perhaps, Gatsby can be viewed as being his own father: after all, at the end of the novel, Nick remembers Gatsby standing outside his "ancestral" home. Either way, unlike Nick, whose aunts and uncles talk over every step of his career, Gatsby has no family to disappoint.
The novel is full of characters who are, by most standards, immoral people: