Why don't Proctor want Mary to go back to court?

Answer 1

John Proctor and Mary had a brief affair, Mary is in love with John Proctor and when John tells her that he made a mistake and has no intention of ever leaving his wife for her Mary feels betrayed. Since she cannot have John she will revert to any action which will bring harm to him or especially his wife Goody Proctor. John seeks to protect his wife from potential public humiliation in attempting to discredit Mary and prevent her from taking the stand.

Answer 2

Proctor does not want Mary to go back to court because he fears for her safety and worries that she will be in danger if she testifies against Abigail and the other girls. He also believes that the situation in court has escalated beyond their control and fears that Mary's testimony may not be enough to save them.