It's a common mistake made by some that the slavery mentioned in the Jewish Scriptures was anything like the slave trade during Roman times or the Atlantic (sometimes called "African") slave trade.
The Torah forbade any type of slavery that resembled what the Jews experienced in Egypt, and it was nothing like the slavery of recent times, like those owned by Americans before the Civil War. For instance:
1. Slaves in Israel became members of the household, and enjoyed the benefits and protections of the Mosaic Law such as rest on the Sabbath, rest and celebration on Jewish holy days, and thus could inherit the household's wealth and name if there was no heir to pass it to (and possibly in despite of that fact according to Proverbs 17:2).--Ge 15:3; Ex 12:44, 45, 20:10, 21:20; 23:12; Deut 5:14-15; 12:18; 16:11-14.
2. Slaves were compensated for their work, especially when they were hurt on the job. Mistreatment by the owner could even be a reason for immediate release. If a slave died from mistreatment at the hands of their owner, the Torah demanded that the slave owner face punishment for killing another human.--Ex 21:20, 26-27; Lev 25:29, 43, 46, 53; Deut 23:17.
3. Slaves could buy and own their own property. They could even buy their freedom from their masters.--Lev 25:29; 2 Sam 9:10; 16:4; 19:18-30 (see also 1 Sa 9:8); see also Jewish works Kid 1:3; Yad, Avadim 5:2.
4. Those who owned slaves were forbidden by Torah to mistreat them, and kidnapping someone for the sole purpose of enslaving them or selling them into slavery was a capital offense.--Ex 21:16; Lev 25:43, 46, 53; Deut 23:17; 24:7.
And there's more. But this should be enough to demonstrate that the service regulated by the Torah in Scripture is not the same as the slavery developed by Gentiles and employed in recently modern times.
Too often upon leaving the Watchtower or never studying anything but a Christian interpretation of Torah, people are left reading Jewish texts through Western filters. The same often applies in other areas of Jewish writings as well.