In the end, you gotta do what you think is right, but even Jesus stopped answering his accusers eventually. There will eventually come a point of realization that nothing you say will make the blindest bit of difference to him or your relationship with him. There's a very good reason for that, and if you don't know it now, you soon will.
As for damage to others who might be deceived by him, I think most boarders are familiar with his antics by now. He plays the role of martyr too well to ever be derailed from the course he has chosen for himself.