Fabulous points, TomP2. In my view, you've hit the nail on the head. I am especially struck by your taking up the idea of "proof"--enough so to brave these choppy waters, which I have been reluctant to do of late.

I'm not sure that proof is possible here. It seems to me that some of the very same passages quoted in support of what I confess sounds to me like the Willoughby-as-dastardly-villain theory can be, and by some are, interpreted differently, in line with what I'll call the Willoughby-as-flawed-but-human theory (and vice versa). Moreover, I question the desirability of such proof. Indeed, it seems to me wholly beside the point.

To my mind, the brilliance of Austen's depiction of Willoughby is the very slipperiness of his character. His is an uncertain, impulsive, and unreliable temperament (to say the least). She seems to have intentionally written him this way, rather than tidy up loose ends, which she easily could have done. While it can be tempting to exile him to irredeemable nastiness, I personally find it more rewarding to engage the very human coexistence of inconsistencies he embodies so radically. Call it the tragedy of his failed potential, if you will, on which Elinor muses during their talk at Cleveland:

“Her thoughts were silently fixed on the irreparable injury which too early an independence and its consequent habits of idleness, dissipation, and luxury, had made in the mind, the character, the happiness, of a man who, to every advantage of person and talents, united a disposition naturally open and honest, and a feeling, affectionate temper. The world had made him extravagant and vain--Extravagance and vanity had made him cold-hearted and selfish. Vanity, while seeking its own guilty triumph at the expense of another, had involved him in a real attachment, which extravagance, or at least its offspring, necessity, had required to be sacrificed. Each faulty propensity in leading him to evil, had led him likewise to punishment.”