Nowhere does the Bible condemn slavery. Jesus himself endorsed the beating of slaves, even when they make an honest mistake so that they won't make it again. It may interest you to know that Darwin's most heated arguments with Captain Fitzroy (the fundamentalist Christian captain of the Beagle) were about slavery not biology. Darwin thought it to be a disgusting practice that demeaned the humanity of both slave and slaver, whilst Fitzroy supported it, claiming Biblical support.
I note that you fail to address the Biblical instruction to hold bond-servant's family hostage against the decision of a bond-servant to become a permanent slave. I also note that you fail to address biblical endorsement for sex-slavery.
The slaves that you say Americans bought fair and square were mostly kidnapped, and as such do not compare with a 'bond servant" agreement.
I have checked this with an academic historian who specialises in this subject and your statement is simply untrue. The overwhelming majority of slaves shipped from Africa to the New World were bought in African markets from African slave-holding chiefs. Sometimes these would be surplus population from the chief's tribe. Kidnapping in such huge numbers would have been dangerous, expensive, and difficult, compared with simply buying the slaves in African markets.
I do however find your "fair and square" phrase bewildering. Slavery disgusts me even when it is practiced in forms that are permitted by the bible, such as the legitimate purchase of non-Hebrews in slave markets. It is only you that should see the buying and selling of human beings as something that could be "fair and square".
I don't disagree in principal with corporal punishment as I have already stated. But I find the idea that a bond-master or slaver can be the sole arbiter of such punishment for bond-servants or slaves completely unnacceptable. Evidently you don't, so we are worlds apart on that one.
The Bible states that if such beatings result in death delayed by more than 24 hours from the punishment then no offence has occurred. This sounds like an invitation to make extremely violent bloody beatings to me, as long as the poor wretch clings to life for 24 hours. A sadist's charter. F Douglass may have said that the Bible doesn't require masters to be bad masters, but it doesn't seem to require them to be good either if the life of a slave is to be viewed so cheaply.
Still at least you seem to be true to your faith and your Holy Book on this one. Evidently you view slavery as an entirely acceptable human state.
Bible Law says that if a master beats a slave and the slave dies within a day then the master is guilty. You use that to accuse God of being unjust. Those of us who are able to examine things in perspective understand that this rule was given in times where slaves could be beaten to death with no consequences whatsoever. This law was meant to limit punishment of slaves, not promote it. You instead take this to mean that God should be condemned for advocating that masters be allowed to use any force at all. There were thousands of captive aliens in Israel. There were bond servants who stole from their masters and beat their fellow servants. Perhaps you think the U.S. military should not have been allowed to use force to manage the tens of thousands of prisioners in our various wars.
Warfare slaves aside, how does one control an anti-social individual who does not have the skill set to successfully navigate civilized society? The Bible says he can become a bond servant to a master (of his choosing if he is an Israelite) who has authority to punish him. Other than that it is about like a seven year contract in the armed forces. At the end of the seven years perhaps he has learned enough to go out on his own, or maybe he realizes that he needs the structure and likes things with his master.
Secular humanists (such as yourself apparently) say that is too inhuman. Instead we must lock this same individual in a cage for seven years, taking more of his freedom than slavery ever could, with other more hardened criminals. After seven years of learning/getting beatings from them rather than a responisble member of the law abiding community, we release the now hardened criminal on an unsuspecting public until he murders someone and the police have to shoot him.
God is just, and his ways are above our ways, praise His Holy Name. Will you continue to mis-use the scriptures in a vain effort to condemn God, or will you use them to find forgiveness and healing from the condemnation that a just God must put on you?