Literary critic: Often the heirs of a successful writer decide to publish the manuscripts and the letters the dead writer left behind, regardless of the merit of the work.
Conclusion (Hence)
A successful writer who decides not to publish a recently completed manuscript should destroy it immediately.
Evidence
Often the heirs of a successful writer will decide to publish any manuscripts they can find, even though many writers have manuscripts they would not like to be publicly associated with even after they die.
Evaluate
The problem the author identifies is that if you're a famous writer, then when you die, your family might be tempted by the "money grab" of selling off any of your unreleased material. But what if you hate this unreleased material and would be mad to know that your relatives let the world see this crap with your name attached to it?
The author then moves to a pretty drastic solution -- if you're a successful writer and you recently finished a manuscript that you decide not to publish, then you should destroy it immediately so that your greedy heirs can't posthumously embarrass you with it.
Isn't there a more moderate prescription that would work? Couldn't you label it with a Sharpie that says, ? Couldn't you modify your will to say, ?
Goal
Let's look for an answer that would make this sound like bad advice, a reason that a successful writer should not immediately destroy a manuscript they just finished but don't plan to publish.