Malbim: There are three kinds of evils that come via people. Those who do not exist are free from all of them! (a) The strong rules over the weak. He incarcerates him in a pit and forces him to do harsh labor. (b) One at a higher level rules over people below him - the rich over the poor, and the esteemed over the lowly. (c) Refer to 3:19:2:1.