Who does Foster accuse of teaching writers to encode sexual messages in their writing and of teaching readers to decode sexual messages in literature?

Freud is the culprit.

So how did all this smutty thinking find its way into world literature?

Blame it on Freud. He put it there.

More accurately, he found it and showed it to the rest of us. When he published The Interpretation of Dreams in 1900, he unlocked the sexual potential of the subconscious. Tall buildings? Male sexuality. Rolling landscapes? Female sexuality. Stairs? Sexual intercourse. Falling down stairs? Oh my. All of this may be regarded these days as so much hokum in the arena of psychoanalysis, but it’s like gold in terms of literary analysis. Suddenly we discover that sex doesn’t have to look like sex: other objects and activities can stand in for sexual organs and sex acts, which is good, since those organs and acts can only be arranged in so many ways and are not inevitably decorous. So landscapes can have a sexual component. So can bowls. Fires. Seashores. And 1949 Plymouths, one supposes. Virtually anything, if the writer so decides. Oh yes, Freud taught us well. And some of those he taught are writers. Suddenly, as the twentieth century gets rolling, two things are happening. Critics and readers are learning that sexuality may be encoded in their reading, while writers are learning that they can encode sexuality into their writing. Headaches, anyone?