The Reluctant Fundamentalistis essentially one long monologue. The speaker, Changez, tells his American listener a story. This story/monologue is divided into the story itself and the interaction between Changez and his American listener. Part of this dual nature of the novel is that the reader gets Changez's story with the uneasy reactions of his American listener.
With Erica, Changez sees the best in America. With most other aspects of American culture, Changez drifts more toward an anti-American ethos. Drawing from this parallel, Changez wants to love America (Erica - note the similarity of the words: AmErica) but that love is never fully reciprocated. Changez's and Erica's possible, but inevitably impossible, love affair is indicative of the troubled relationship between America and Pakistan. He wants to love America but is pushed away. As this parallel can dissolve into a political or ideological debate, each reader might interpret the novel differently. Perhaps, both Changez and Erica (East and West) are to blame for the lack of a good relationship.
Changez is somewhat happy about the 9/11 attacks and he also faces persecution following the attacks. In other words, there is a historical, tenuous relationship between America and some Middle Eastern countries and the attacks provoke that troubled relationship. Although it is deplorable that Changez reacts with a smile, following the attacks, his reaction is based upon this historical relationship, some of which he discloses to his American listener. While it is wrong for him to react this way, consider that his reaction is based upon a much larger, historical political struggle. Changez tries to love AmErica, but that history and his experiences in America turn him the other way.
Overall, the title says it plainly. Changez did not want to be a fundamentalist. He feels that his circumstances drove him there. One might admire his attempt to be more American but one might also admire his loyalty to his roots. Changez goes through "changes." To an extent he has embraced and achieved the American Dream (certainly with his job at Underwood Samson) but ultimately, he is disillusioned by it.
Changez treats his American listener with respect and speaks with calm logic. But it is the American's reactions which cause the reader to reconsider Changez's motives. In the end, it is unclear who is the aggressor. This is a microcosm of the larger political problems between the East and the West.
Any text is open to the reader's interpretation. Texts such as this one are even more ambiguous because they provide dualities and closure which the author does not completely resolve, leaving that work for the reader.