Enslaving a person by stealing him from his life is a capital offence. So often Atheist cherry pick the bible in an attempt to invalidate the authority of God’s word. 

Exodus 2:16 And he that stealeth a man, and selleth him, or if he be found in his hand, he shall surely be put to death.

They neglect to read verses that speak directly against the abuses of humanity.  Applying their logic, the Banks are the worst institutions in history.  People sell their lives to serve the Banks.  Some live their entire lives under the taskmasters we call banks.  

The bible is clear that slaves had to be part to the decision to become a slave.  This was at times, due to convenience, such as our modern loans, but often it was to clear a debt or a penalty for stealing or negligence.  In part, this is still the framework in much of our legal system today.

Jacob (Israel) enslaved himself for 7 years and yet again 7 years to abtain a wife.   The bible is clear that loaning was to be for 7 years and then the debt was to be cleared and the slave freed unless he chose otherwise.

It is crystal clear, that slavery in America was and is immoral.  One must understand that there is a biblical construct and clear roles for what our society calls Banking and Criminal Justice.   The Bible in no way supports the abuses of humanity.  God is not the author of such abuse; Man is!  God will righteously judge the whole of humanity, Nations and the individual.

Any man that takes the life of another, whether spiritually, mentally or physically to enslave them, is not walking with God.  Jesus hates the teachings and the deeds of the Nicolaitans.  Revelation 2:6&15.

Greek: Nico (victory) + laos (people) more specifically, the laity; meaning "lay conquerors" or "conquerors of the lay people".

Exodus calls for the death of slave traders!