People nowadays interchange gifts and favors out of friendship, but buying and selling is considered absolutely inconsistent with the mutual benevolence which should prevail between citizens and the sense of community of interest which supports our social system. According to our ideas, buying and selling is essentially anti-social in all its tendencies. It is an education in self-seeking at the expense of others, and no society whose citizens are trained in such a school can possibly rise above a very low grade of civilization