It the nature that keeps to maintain a balance on earth...if there wud have been no slaves ..WHO WOULD DO THE WORK ..in my opinion it is a necessary evil....yes i may consider it as an evil...why would someone think that he is superior than the slave..after all they both have the same meat , same blood ,same brain & the same heart....it is actually the nature who tries to make a balance in order to atop chous in this world ..but hurting slaves , or having a thinking like i am superior than a salve is totally non humane .....