“Well, that’s your opinion, and my opinion is that aunt Sally’s the key”?

Prompt (1 pg. minimum): Imagine: in an American Literature class, a particularly whacky student insists that Moby-Dick is not really about whaling at all but is rather about his elderly Aunt Sally, who lives in Passaic New Jersey. Without reference to intention of Herman Melville (the author of Moby-Dick)—who obviously could never have encountered, much less decided to write about, anyone who is alive today—how can you respond to this student without him saying “Well, that’s your opinion, and my opinion is that aunt Sally’s the key”?