Roth's sense of humor is very dry. If taken at face value, this novel is about a hopeless kid who can't figure out why he feels crazy. However, since the novel was authored by the famous Philip Roth, the reader should probably interpret the novel as a joke. In fact, the novel is extremely popular among comedians for exactly that reason.
Viewed as an work of dark comedy, the novel comes into focus. One reason to take this novel with a sense of humor is that the psychological dilemma defined at the beginning of the novel is really quite simple, in psychological terms. Basically, the kid is just repressed. Because he feels like he is being judged with harsh moralism, he doesn't have enough grace or patience for himself to accept himself the way he is (and in fact, he is being judged—but only by himself). In other words, he feels like he should be embarrassed by his sexuality.
We're psychoanalyzing the main character, not only because it is a helpful technique for analysis, but also because the plot indicates that Roth wants us to do exactly that. This novel could be set in many ways, but Roth chose to invite psychoanalysis by setting the novel within a session of psychoanalysis.
Also, there is the issue of vulgarity. The novel was criticized for its use of obscenity, but the novel itself is about the shame the young man feels about the vulgarity of his own sexual appetites. Maybe the reason Roth included this feature is to show which readers are still operating from this pathological type of moralism.
In other words, he might be literally trying to offend people, because he is offended by moralistic people, and he wants to put them in the therapists seat by showing that secretly, the novel is about anyone who might be offended by its language.
