From Beginning of the Holocaust (#172) by Rabbi Avigdor Miller
Q: Why Did the Torah Permit Slavery?
A: Now let’s understand that we’re living in a time when all the standards are measured by the fad of the day. Slavery is today considered as something to be abhorred, but you have to realize this wasn’t the case in ancient times among Jews.
First of all, among gentiles in ancient times, what should a person do who had no livelihood? He had no land. Land was passed on from father to son. Suppose you had no land, you had no family, you were a stranger, what should you do? You would die of starvation. So Eliezer eved (servant of) Avraham who wanted to become a loyal disciple of his great teacher, what did he do? He gladly became an eved (slave).
In those days to become a slave meant you joined the family in a certain status. Hagar gladly became a shifcha (slave-girl) to Sarah; it meant joining the family. She was a member of the family. In those ancient days, in cases where the woman, the ba’alas habayis (mistress of the house) was childless, she gave her handmaiden to her husband and he had children from her. That’s how it used to be way back before the Torah was given. Slavery had a different face in the ancient days.
Among Jews slavery meant that a person became a member of the family. First of all a slave had to be circumcised. He had to go for tevilah (ritual immersion) and become a Jew in a certain sense. All slaves had to keep the Torah. A slave couldn’t be beaten, because he could have recourse to the dayanim (judges). And if a person was careless — even when he had to chastise a slave, even if he was hitting him for a reason — if he knocked out a tooth, or some other one of the twenty-four chief limbs, then the slave could march out a free man. If he killed a slave, the owner was put to death. Among Jews, slavery was an institution like the family.
You can judge [the Torah’s slavery] from the following. Suppose a Jew bought a slave who refused to circumcise, so the Jew could say to him, I’ll sell you back to the gentiles. That was considered a threat. And in almost every case the slave was willing to circumcise. Slavery was an institution that fit into the social structure of Jewish life and the Jewish slave, even the eved Canaani (Caananite slave), to some extent, lived a privileged life and he was protected by the Torah. Therefore there is no question that slavery should have been sanctioned, as it was, by the Torah.