It would simply seem understandable that our Teacher would not have agreed to hold a discussion, debate, and the like, if the Torah was really given to him by God, and to allow atheistic views—or say, the mixed multitude, or the two sorcerers who made the calf, or Dathan and Abiram, or Korah—to express opinions against him.
That doesn’t seem likely; otherwise, why did he ask God that the earth swallow Korah instead of dealing with them through convincing arguments?