Reformed Covenanter
Cancelled Commissioner
"On what authority do you say these things?" Christ implicitly puts the question back on the Pharisees by asking them to justify their rejection of John the Baptist. They are silent and embarrassed because they don't have a legitimate authority to rule against John, and they know it.
Some weeks ago I met two atheists. One took my Bible and started flipping through it. I think I just asked him, "So what dastardly deed done by God or by a saint are you looking for?" I know that they like to argue by claiming just what a moral monster God is (Cue "Oh Patrick..."). He finally reaches Elisha calling the bear to maul the 40 children. He talks about how severe and wrong it is, then I just ask, "On what authority do you say that?" I watched these two guys spin themselves in a circle for at least a half hour trying to defend an absolute judgment on the work of Elisha while not having a definite authority for their judgment. Oftentimes such peoples end up saying, "I am my own authority." The rabbit hole gets deeper from there.
Presup one time also made a good lead-in for evangelizing vegans. "On what authority do you say these things?"
How is what you are saying really any different to the moral argument for God's existence?