You might want to throw out the Luther "invented his theology to support his masturbation habit" too. Many people believe Luther's theological concepts based upon a Scriptural understanding. You may disagree with that standing. But, what was said about it was a bit across the lines of, uh, etiquette.
I think you would agree that whether many or few believe certain thing does not make it true or false. I think that Luther and his collaboratiors in the Reform movement succeeded in forming a theology that generally is accomodating human error, encourages schism, and is in sync with the modern times. This is because of the notions such as salvation through faith alone, anticlericalism, antimonasticism and sola scriptura, and various variants of surety of salvation. These theologies fit the modern man, so whatever scant scriptural support there is for them, the modern man clings to it. This is what makes him what he is.