I think that this is a fairly powerful element in the drama.  Much of it is going to be dependent on how one sees Troy, as a father.  If one wanted to see him in a sympathetic light, then Troy seeks to protect his son from the same pain of deferral and denial that he experienced.  Cory's dream of playing football is something that strikes home with with Troy, as he wished to play baseball.  In order to minimize the pain that he experienced with this dream's denial, Troy could be seen as demanding that Cory surrender his dream because of this.  In this case, the father is protecting his son from the same demons that plagued him.  If one wanted to see Troy in a more skeptical light, then his actions are done out of spite.  In this paradigm, Troy is more angry that his son is going to have the chance to do what he, himself, could not do and his insistence on Cory to submit to his will and the lack of understanding he shows towards his son living out his own dream could be seen as evidence.  Troy is so bitter with the direction of his own life that he is incapable of allowing anyone else from living a life that is not filled with the same resentment and anger that lives with him.  Troy's actions towards Cory can be seen in either light, depending on how much sympathy Troy evokes in the reader/ audience.