In "The Crucible," why did John Proctor decide to tear up his signed confession?

All throughout the play,
John Proctor has thought of himself as a "fraud," a word he uses to describe himself
in the fourth act when he is considering whether or not to confess to witchcraft and save his
life.He cheated on his wife with their household help, a seventeen year-old girl named Abigail
Williams, and then he failed to tell the court what he knew about her deception until after it
was too late and hysteria had taken hold of Salem.In one sense, it is absolutely possible to
consider him at least partially responsible for the tragedies that take place in the
text.

In the end, John asks his wife, Elizabeth, to forgive him for what he's
done.He wants her to absolve him, but she sagely says that her forgiveness would not matter
"if [he'll] not forgive [him]self."She confesses that she, herself, feels guilty for
her behavior within their marriage, and they have such a beautiful moment of truthfulness and
love that John wants to stay alive to be with her, and he says that he will confess to save his
life.However, he must first lie, and do so in front of Rebecca Nurse, whose conscience would not
permit her to lie.Then he is asked to name other witches, but he refuses.Next he is forced to
sign the document on which his untrue confession has been recorded.He learns it will be made
public, and he wonders how he can teach his sons to be men if he "sold [his]
friends."Suddenly, in tears, he crumples the confession and tears it up, telling his
persecutors,

You have made your magic now, for now I do
think I see some shred of goodness in John Proctor.Not enough to weave a banner with, but white
enough to keep it from such dogs.

He has finally learned
to see himself as a good man, someone who can be redeemed by keeping his integrity, but he can
only do so by refusing to lie now.Therefore, he tears up his confession.