On Satire

I'm always ambivalent about the use of the idea of satire to defend objectionable works. Who determines whether a work is successfully satirical? If a piece of art, or writing, or music, still appeals to the people it is meant to be satirizing, does it then unequivocally fail at being satirical?

What about the author or artist? Does the ambiguity of the work's earnestness cast a light on the author's intents, or just on her/his ability to execute what is admittedly a very difficult genre? It's a knotty matter.