Avi Billet writes:
1. Slavery in the Torah is nothing like slavery we envision. Many rules were put in place that protected the eved (certainly the eved ivri), including that certain injuries inflicted by the master would set the eved free automatically.
This is useful apologetics, but does not get beyond apologetics. I see no reason not to say that this is a case where the Torah speaks ke-neged yetser ha-ra`. It is a concession to the social-political framework of the time.
R. Kook (Iggerot I #89) moves in this direction but also presupposes the racial inheritance of acquired characteristics. The combination of the former and latter elements is quite complicated and, for that reason, somewhat problematic. See also R. Kook's discussion about Tavi the slave of R. Gamaliel in Ein Ayah to Berakhot ch. 2.
R. Kook also makes the argument that under certain circumstances, alvery is more humane than sweatshop labor or coal mining because the master has a stake in the welfare of his slave whereas the factory owner can simply dismiss a slave with black lung or TB and let him die. This argument was popular in the American South, which does not make it a better or worse argument.
On subjects marginally connected to this see my Orginof Nations and the Shadow of Violence (Tradition, Winter 2008? and Orthodox Forum volume on War and Peace);
"We Were Slaves to Pharaoh in Egypt" (Hebraic Political Studies 4:4)
and
"Why Should a Slave Want to be Free" (Mishpetei Shalom, Saul Berman Festschrift)