why does Judge Danforth refuse to pardon those who are scheduled to hang that day? What is problematic about his reasoning?

Danforth needs the hangings to validate the court's existence and authority. If the people confess to witchery, the court can save face and show mercy upon the convicted. Proctor, however, will not give away the only thing he has left: his name. forcing people to confess destroys any credibility the court has. The people will eventually revolt.