Holden considers that his older brother has sold himself out by sacrificing his artistic talent to acquire bourgeois status and a comfortable life. The reader cannot know, though, if this is really true or not since Holden is not exactly a reliable narrator. To him most everybody is "phony" and it seems as if Holden is subconsciously jealous of the success he himself has not attained. Since success is beyond his reach (or at least for the time being), he give it and most everybody associated with it "the sour grapes treatment."
The relationship between Holden Caulfield, the protagonist and narrator of J.D. Salinger's novel The Catcher in the Rye, and his brother D.B. is more complicated than to simply suggest that the former held the latter in contempt. While Holden makes very clear that he believes that his brother sold out for monetary gain and fame, he also respects D.B.'s abilities and seems to fondly recall many experiences involving his older brother.
When contemplating Holden's relationships with others, especially his family, it is important to keep in mind precisely what The Catcher in the Rye is about: youthful alienation. Salinger's protagonist is the reigning symbol of alienation and a component of being alienated from society at large is contempt for that society. Holden has little good to say about many individuals in his narration. All things considered, what he has to say about D.B. is not that bad. In the novel's opening chapter, Holden introduces the reader to his current station in life and to his brother:
"He's in Hollywood. That isn't too far from this crumby place, and he comes over and visits me practically every week end. He's going to drive me home when I go home next month maybe. He just got a Jaguar. One of those little English jobs that can do around two hundred miles an hour. It cost him damn near four thousand bucks. He's got a lot of dough, now. . . . It killed me. Now he's out in Hollywood, D.B., being a prostitute. If there's one thing I hate, it's the movies."
So, the reader quickly learns that D.B. is, to a certain if undefined extent, a caring brother. We also learn from this passage that Holden believes commercial success at the expense of artistic integrity is tantamount to treason. Later, Holden notes that "my favorite author is my brother D.B., and my next favorite is Ring Lardner." Yet, Holden repeatedly returns to the notion that his brother has sacrificed his integrity for fame and profit: "Ernie's is this night club in Greenwich Village that my brother D.B. used to go to quite frequently before he went out to Hollywood and prostituted himself."
In short, it is unfair, one could argue, to conclude that Holden is contemptuous of D.B. Salinger, and presumably his protagonist, is aware of the history of the relationship between the literary community of New York and the film industry of Southern California. Fitzgerald, Faulkner, and Steinbeck all worked on screenplays, and few would consider any of these esteemed authors sell-outs. More likely, as noted, Holden's repeated characterizations of his brother as a prostitute is a product of the aforementioned sense of alienation, and of the moral and intellectual superiority that often accompanies alienation. After all, in the novel's final passage, Holden acknowledges, with reference to the world of sell-outs or "phonies," "D.B. isn't as bad as the rest of them." Brotherly love is there, commercial success or not. Holden, one can surmise, knows that D.B. is a good person, even if his priorities are suspect.
Holden has contempt for his older brother D.B. for complicated reasons. First, it should be noted that Holden has a lot of respect for D.B.'s writing abilities. D.B. had once been a writer of short stories, penning a collection called "The Secret Goldfish" which Holden greatly appreciated; thus, the fact that D.B. has (in Holden's eyes, at least) sold out on his talent to become a screenwriting hack in Hollywood is astonishing. Holden thinks that actors and movies themselves are phonies and that working in film is not a worthwhile pursuit for D.B.
Holden also despises the fact that D.B. is raking in a ton of money by writing for the movies. Holden sees this not as real work, but rather as an act of self-degradation. He, thus, compares D.B.'s new profession to that of a prostitute.