There is no strength in it. Labor without joy is like a life without The Source of All Beauty and All Life. There is no wisdom in it. Joyful labor is a special quality which permeates all that it touches. Joyful labor is quality labor.
Joyful labor is positive action.
Joyful labor is prudent labor. Like it has been stated, the argument against joyful labor is mentally convincing, emotionally satisfying, and leads to pain.