Many Christian apologists will not accept the idea that biblical slavery in the Old Testament was indeed slavery. They think it was all voluntary indentured servitude, or something like it. Here's a quote from A History Of Ancient Near Eastern Law on slavery (emphasis mine):
A citizen could not be enslaved against his will if independent or
without the permission of the person under whose authority he was
if a subordinate member of a household. The only exception was
enslavement by court order for commission of a crime or civil wrong. Although in practice economic circumstances would often force a person into slavery, in law his act was, strictly speaking, voluntary. The foreigner, by contrast, could be enslaved through capture in war, kidnapping, or force, unless protected by the local ruler or given resident alien status. In the latter case, protection still might only be partial. As a proverb puts it: "A resident alien in another city is a slave."
To drive the point even further so that there is no confusion over whether this applied to Israel:*
184.108.40.206 Foreign slaves could be acquired by war, purchase, or birth. If a besieged city accepts the offer to allow their surrender, the people serve as tribute labor (Deut. 20:11). Should the city not surrender, men should be killed at capture rather than turned into slaves; women and children can be taken as booty (Deut. 20:12-14).
220.127.116.11 Foreign slaves bought from the surrounding nations or from foreigners living in Israel do not go out: they are inherited as property (Lev. 25:44-46).
The Christian or Jew who wishes to deny that some Biblical slavery was indeed real life slavery, little different from the kind we had in the antebellum South, and condoned by their god, Yahweh, is in utter denial.