What is John's excuse for confessing in Act IV of "The Crucible"?

In Act IV of the play Elizabeth and Rev. Hale try to convince  John to confess to witchcraft.  Rev. Hale really does not do much to change John's mind but when John and Elizabeth talk privately, he begins to think about his life.  He realizes that he has already sinned by having an affair with Abigail and decides that it would not be much of a stretch for him to commit another sin by lying.  Therefore, he decides that he will confess to witchcraft. 

After he does this, Danforth forces him to sign a written statement of confession.  In response to this, John decides to take back his confession saying that he can not sign his name to lies basically because he will be defaming his name.  He states, "Because it is my name! Because I cannot have another in my life! Because I lie and sign myself to lies! Because I am not worth the dust on the feet of them that hang! How may I live without my name? I have given you my soul; leave me my name!"