I see this argument come up often here...the fact is, slavery in Bible times was much different than the slavery we are familiar with today, as J Wallace brings out...
J. Warner Wallace is interviewed by Brittany Valadez about the nature of Ancient Near Eastern slavery and the claim that the New Testament authors condoned slavery. Was slavery, as it existed in the time of the New Testament writers, the same as the form of slavery that existed in the New World (like slavery in the United States)? Why would the Bible fail to wholeheartedly condemn any form of slavery?