I cruised through the first half of the novel, and then set it aside for a couple of weeks. As I read the second half, I found it somewhat challenging to reconstruct what had happened earlier. In some ways, I think my experience gets at a fundamental element of the novel: there is Fowler's life with Phuong and without Pyle, and then there is his life with Pyle. They are very different lives.
To put it bluntly, Pyle is a painfully obnoxious character. Greene does a brilliant job of showing Pyle's earnestness and righteousness as offensive qualities. Pyle is a New England Puritan who believes that Phuong should be treated a particular way. That's to say that Pyle wants to Americanize her, and thereby raise her out of what he sees as her benighted state. He thinks the Vietnamese are childlike, and his condescension is palpable. But unlike other versions of American superiority in the novel, Pyle's is complicated by his apparent innocence. What comes out clearly is that those who are innocent, righteous, and earnest are more dangerous than those who explicitly claim and try to impose their superiority.
Greene does an excellent job of making explicit the formula for imperialism: the desires or deaths of indigenous people matter much less than the abstract good the colonizers think they bring. To put it differently, Pyle and his kind think that losing a couple thousand Vietnamese as "collateral damage" is a cost worth taking if it leads to a Vietnamese society arranged on an American plan. In The Quiet American, the names of the colonizers appear to be changing, but regardless of the names, the Vietnamese are still the colonized.
I think Greene does an excellent job of showing, in Pyle, the ability to compartmentalize one's experiences and beliefs. Pyle imagines Phuong as the mother of his children, and earnestly desires her as a companion. He lectures Fowler on appropriate relations between men and women. And yet, Pyle has no compunction about being part of a plan that kills women and children. These two things take up different parts of his brain, and he keeps them separate. I think the novel shows that this kind of mental and emotional distinction is possible if one sees people as abstractions. The Vietnamese are an abstraction, and Pyle does not care about them, only about the desired political outcome. Phuong is a real person, and he sees her differently--but in the end, he sees her as an object to be raised up into a state of American "civilization."