"From the human point of view, return paid to non-human factors of production is unearned. ... The employment of capital instruments and natural resources in economic production requires no personal hardship or exertion from any human being. The economic services provided by these factors of production are not corporeally inherent in human beings. The opposite is true of labor services, which can only be provided through the physical and mental activity of human beings. ... The really grossly exaggerated personal incomes in society are dominated by property income, and this source of inequality would be abrogated by the equalization of property income distribution."