They know their church's interpretations of the Bible, but they don't know the underlying text. This is ironic since many Christians claim that prima scripura or sola scriptura is important to them. Sola scriptura clearly states that interpretations of scripture have less authority than the scripture itself. [2] [3]
44 “They also will answer, ‘Lord, when did we see you hungry or thirsty or a stranger or needing clothes or sick or in prison, and did not help you?’
45 “He will reply, ‘Truly I tell you, whatever you did not do for one of the least of these, you did not do for me.’
46 “Then they will go away to eternal punishment, but the righteous to eternal life.”
This isn't even a debate, the Bible has very clear support for slavery. [2]
In the Old Testament, foreign slaves could be held as life-long personal property (ie. chattel slavery), see Leviticus 25:44-46. Foreign slaves who were female were treated especially harshly, see the last three paragraphs here.
The New Testament is slightly less clear about its support for chattel slavery, however there's still extensive discussion of exactly when and how a slave could be freed, suggesting that someone could be enslaved for long periods of time.