I think most Biblical slavery is "involuntary" though a poor man may sell himself into slavery for a fixed period.
That verse in Exodus 21:16 speaks to the kidnapping or theft of a man's freedom.
Take a look at this (an keep in mind that Leviticus was written after 538 BC--i.e. very old)...
Leviticus 25:44-46Here are ALL the verses on slavery in the Bible. LINK to slavery in the Bible.
English Standard Version (ESV)44 As for your male and female slaves whom you may have: you may buy male and female slaves from among the nations that are around you. 45 You may also buy from among the strangers who sojourn with you and their clans that are with you, who have been born in your land, and they may be your property. 46 You may bequeath them to your sons after you to inherit as a possession forever. You may make slaves of them, but over your brothers the people of Israel you shall not rule, one over another ruthlessly.
Wow..thank you..
And since the crucifixion all who will accept Jesus are our brothers no matter their race or nationality. NO MORE SLAVERY.