In Graham Greene's The Quiet American the topics of innocence and naivete are in constant and direct conflict with the reality and crudeness of war.
In the novel, innocence is embodied by the character of Pyle. An extremely idealistic and naive American, he represents the innocence of the inexperienced who are exposed too early in life to a situation as concrete as a war in the battlefield. Young and abstract, Pyle is a dreamer who consistently aims to search for the positive in everything. To give his character a very ironic twist, Greene exaggerates his persona by making Pyle overly trusting, which in turn makes him look almost silly. This is what gives the novel a somewhat anti American curve, since it is the American soldier who is portrayed as naive and "innocent" enough to put himself in a weak position and ending up dead in battle.
His foil, which is the character of Fowler, is basically fed up with Pyle's ideal notions of war and consistently criticizes him. He foreshadows that Pyle's innocence will eventually endanger since it basically will render him more and more vulnerable. In the end, Fowler is correct. He blames innocence for the death of Pyle, and he speaks of innocence as if it were a curse, and not a virtue.
Therefore, in what Greene intends with his treatment of the topic of innocence is to explain how, in the battlefield, even the good turns bad. War could test the kindest of men, and it will be War who will win. In the battlefield it is about survival and not idealization. It is about being in control and fighting to live, and not about questioning life or death. Hence, in this story, innocence is simply a very dangerous thing to hold on to.
This question goes to the very heart of the compelling issues that are raised by this novel. Important to realise is the way that Greene uses characterisation to embody the qualities of innocence and experience, which he then associates explicitly with the naivety of America and the cynicism of the waning Imperial power of Britain. It is Pyle of course who is the American representing innocence and naivety in the way that he wants to become involved and is so eager to rush in and take sides. This is of course in complete opposition to Fowler, whose mantra in the novel seems to be "I'm not involved, I'm not involved."
The action in the novel, and the way in which Fowler is forced to take sides however and act against Pyle, leaves us with a rather ambiguous ending. Although Fowler gets the girl and manages to rid himself of his opponent for her affections, it is clear that the final chapter of the novel presents us with a character who is deeply unhappy and unsettled by his experience of meeting Pyle. Although we may be tempted to dismiss innocence in this novel as being a "weaker" force than experience, and point to the way that Pyle is so easily removed by the machinations of Fowler as evidence of this, it is clear that the novel does not allow us such easy conclusions. The ending forces us to ask whether there is something good and valuable in the innocence and energy of Pyle that is lost in the face of Fowler's experience and world-weary cynicism.