When parsing American society, it is very important to keep the idea of appearances in mind. Conceptual realists posit that the world of appearances is mind-independent. That which we think the world to be is something beyond ourselves, but doesn't reach the actual existence of things. So manipulating this shared notion of how things are becomes the game. Baudrillard calls the resulting social world hyper-reality; this was the concept for the Matrix films.
The poet's blue guitar, that thing that changes things as they are, opposes the shared notion of the world that is the basis for this social reality. This isn't inevitable; a culture more inclined to be constantly seeking to determine the way things are, more truth-seeking, as it were, would accordingly value the poet's work in revealing things about the world. But if appearances govern, revelators threaten.