One way in which Holden can be seen as a hero is that he stands against the negative traits of society. Holden does battle against "phoniness" and the hypocrisy that is a part of the modern setting around him. In this light, Holden would have to be seen as a hero because he tirelessly fights against a force of malevolence. Holden might not be certain of much in his life. Yet, he knows his mission as a crusader against phoniness. Another reason that Holden is a hero is because he wishes to stand up for that which is right. He honors his love for Phoebe as one such element. Holden understands that this is something towards which he can pledge his life and his commitment. This is heroic because it shows him to represent something transcendent as opposed to capitulating to the temporal and contingent.
Like many heroes, a case can be made that Holden is heroic because he is misunderstood. Holden is not fully understood by the world around him and he commits himself to his ideals despite the fact that he is not understood. Holden is not the hero towards whom one can immediately move and endorse. Yet, in laying out a case for Holden's heroism, it would reside in how he is pursuing an end that few others understand. Holden wishes to transform what is into what can be and beneath the cynicism is an idealism that can be viewed as heroic. This is the context in which Holden's heroism can be seen.