I stopped watching Glee for the same reason I avoid almost all Christian fiction: as a general rule, Art is buried by Agenda. I am a Christian, and I absolutely support gay rights (an often ham-fistedly presented message on Glee), but I don’t like being emotionally manipulated by art.
In James Joyce’s Portrait of the Artist as a Young Man, the character Stephen Dedalus makes a distinction between what he calls “proper art” and “improper art.” Searching for the relevant passages online, I came across this description from Joseph Campbell:
By “proper art” [Joyce] means that which really belongs to art. “Improper art,” by contrast, is art that’s in the service of something that is not art: for instance, art in the service of advertising. Further, referring to the attitude of the observer, Joyce says that proper art is static, and thereby induces esthetic arrest, whereas improper art is kinetic, filled with movement: meaning, it moves you to desire or to fear and loathing.
Art that excites desire for the object as a tangible object he calls pornographic. Art that excites loathing or fear for the object he terms didactic, or instructive. All sociological art is didactic. Most novels since Zola’s time have been the work of didactic pornographers, who are preaching a social doctrine of some kind and fancying it up with pornographic icing. (Reflections on the Art of Living, p. 246)