this should be the hint that Christianity is not the progenitor of slave morality but given rather an expression of that concept. If Christianity was the primary issue or instigator behind social justice causes then we should be in the most based times ever with it's loss of influence in western civilization. If nothing else, the freeing of the slaves was a rebellion against a religion, christainity, that explicitly told slaves to obey their masters. You can see the same with muslims keeping slaves in arabic countries right now.