Exodus 21

When we see this chapter many are offended that God would allow people to sell others. This would be correct if the selling is what was seen in the context of chattel slavery. The slavery that happened here was when people is when people got into debt and could not pay it back they could sell themselves into servanthood or what would later be called indentured servanthood. They would work for up to six years and then be free to go no matter the amount owed. In fact, later passages require that the person releasing them was to give them resources to start a new life. We also see if any real damage was done to a servant the master was to free them and reimburse them for the damage. There was also an option to continue service to a person for longer which would mean that the owner would now be responsible for the person for the rest of their life even when they could no longer work.

The plan gave a person who made a mistake a chance to repay, keeping their dignity (by paying back) and also knowing that they would be free. It also gave a way for those who needed someone else to keep them secure (the irresponsible, or lacking ability) to find a secure household to join. Before condemning this system remember that thousands of people are currently working at jobs they hate for decades because of debt, especially student debt which can't be discharged through bankruptcy. Where this system broke down is when people stopped following the command God gave. When this happened people weren't freed, slaves were abused, and people instead of being able to have hope had none. This happens every time we don't do things God's way. 

I wouldn't want to go back to this system, but I have to admit if administered as God intended it would be better than how we often handle things now. The reason I wouldn't want to go back to this system is because I have seen humanity's track record and within a generation or two (if that long) what started out as an indentured servanthood would become everything we hate about slavery.