This is my objection to biography as well. The biography of the artist becomes the source of his meaning. Sontag uses the word "content." This "shadow world" of "meanings" is much less interesting that the art itself.
Sontag interestingly ties the idea of interpretation to that of mimesis. Mimetic theories automatically set up art as an inferior copy of reality, whose value is to tell us something about reality itself.
"The task of interpretation is virtually one of translation. The interpreter says, Look, don't you see that X is really -- or, really means -- A? That Y is really B? That Z is really C?"
"Interpretation thus presupposes a discrepancy between the clear meaning of the text and the demands of (later) readers. It seeks to resolve that discrepancy. The situation is that for some reason a text has become unacceptable; yet it cannot be discarded. Interpretation is a radical strategy for conserving an old text, which is thought too precious to repudiate, by revamping it. The interpreter, without actually erasing or rewriting the text, is altering it. But he can't admit to doing this. He claims to be only making it intelligible, by disclosing its true meaning. However far the interpreters alter the text (another notorious example is the Rabbinic and Christian "spiritual" interpretations of the clearly erotic Song of Songs), they must claim to be reading off a sense that is already there."
"The modern style of interpretation excavates, and as it excavates, destroys; it digs "behind" the text, to find a sub-text which is the true one. The most celebrated and influential modern doctrines, those of Marx and Freud, actually amount to elaborate systems of hermeneutics, aggressive and impious theories of interpretation. All observable phenomena are bracketed, in Freud's phrase, as manifest content. This manifest content must be probed and pushed aside to find the true meaning -- the latent content -- beneath."
"In some cultural contexts, interpretation is a liberating act. It is a means of revising, of transvaluing, of escaping the dead past. In other cultural contexts, it is reactionary, impertinent, cowardly, stifling."
"interpretation is the revenge of the intellect upon art."
"To interpret is to impoverish, to deplete the world -- in order to set up a shadow world of "meanings.""