How Do You Deal with Someone Whose Mission Is to Tear Down Everyone Else’s Belief in Jesus?

Questions about how to deal with someone whose mission is to tear down everyone else’s beliefs about Jesus, how to help a child or teen who seems liable to turn away form God due to peer pressures, and how to reach a daughter who says she wouldn’t be a Christian even if it were true.  

• How do you deal with a Christian who has deconstructed and whose mission is to try to tear down everyone else’s beliefs about Jesus?
• What should parents do to help a child or teen who seems liable to turn away from God due to peer pressures?
• How can I reach my daughter, who professed to be saved as a child but now is out of church, in a relationship with a trans man, and says she would not be a Christian even if Christianity were true?