Literary Theory... serious question!

Why do we, as students of literature, impose a structure of implied motives in our analysis by using any of the variegated literary theories, i.e. Feminist, Structuralism, Postcolonialism, New Historicism, Marxism, et al? Shouldn't we first simply read and interpret well to discover what the author is saying and how they are saying it before applying any filters or schemes of application?

I don't understand; it appears that ,in and of itself, literary theory reveals a faulty hermeneutic, it sounds more like textual manipulation rather than textual analysis.

Please help?