I have found that most of the "debators" already know the gospel and many know quite a bit of the Bible. They just prefer to argue and challenge. Also, I have found it best to state the truth one time and withhold myself from back and forth debate unless I am absolutely sure I have something useful to say. I believe it is most important to be full of God's mercies and grace. I just am so sorry to see Christians get all huffed up and storm off. There are many watching and good solid teaching that is full of patience, mercy and grace just might make a difference.