I've been involved in a long thread on the issue of same-sex marriage for a few weeks now. It's going quite well in my estimation as approximately half of my 10 points have seen interaction with the numerous commenters, but none of that interaction has been very successful.
Anyway, today a commenter named Ai Deng has begun questioning me on a tangential, indirectly relevant issue. At first we were wrangling about subjective/objective morality, and now s/he is asking me about slavery.
Ai Deng asked:
Do you consider slavery to be objectively moral or immoral? On what grounds do you base this judgement?
I answered: "Slavery" is too broad to be able to say yes or no. What kind did you have in mind? I'll need a fair amount of detail.
Ai Deng said: I thought it was obvious, but I'm refering to slavery of human beings. Objectively moral or immoral? Grounds?
Sorry, I wasn't specific enough in my question. There have been many instances of human slavery in human history. To which institution(s) do you refer?
As for the grounds I use, I use the objective standard of the Bible, just as a preview. So you might pick out a given instance of slavery, and I'd analyse it in light of biblical moral teaching.
Ai Deng: In not outright condemning human slavery as either moral or immoral, it seems you are leaving open the possibility that some forms of human slavery are objectively morally justified. Would you care to share some instances in which you feel the slavery of human beings is objectively morally justified?
I: The Old Testament form is the only one that comes to mind offhand.
Ai Deng: What is objectively moral Old Testament slavery?
Do you think that it still applies today? I mean, could I own a slave and that would be good and acceptable in god's eyes?
This discussion is beyond the pale of the topic of that thread, so I'm creating this one for Ai Deng's benefit and also to preserve the continuity of other thread.
I am unsure actually what "What is objectively moral OT slavery?" means. Does it mean "What is objectively moral ABOUT OT slavery?" or are you asking what the nature of OT slavery is?
If you mean the former, the God of the Bible is the transcendent and objective source of objective morality. His character is the very definition of good, and He always acts in accordance with His nature. He was the one who revealed the Mosaic Law, in which are found the provisions of OT slavery, so He commanded that that institution be put in place.
Incidentally, OT slavery might be better thought of as indentured servitude for modern parlance, since the laws governing it provide a great deal of rights for the slaves, with limited time of slavery, the limitation of which could be forfeited by the slave, not by anyone else. It doesn't resemble, for example, the slavery of the 19th-century American South all that much, though the word "slavery" leads most people to think that b/c they haven't really looked into it.
If you meant the latter question, check the following links for more information, or better yet, read Exodus, Leviticus, Numbers, and Deuteronomy. Exodus and Deut in particular are not worthy of the typical "bore me to tears" appellation, IMHO. I'd also highly recommend, say, the John MacArthur commentary on Philemon, which is a short NT book.
Here (point 14)
Here (on Lev 25:44 specifically)
Here (also helpful in addressing the 2nd set of questions)
These laws do not apply today b/c they were part of the civil structure of OT Israel, the theocratic kingdom, and we are no longer part of that society. Theoretically, if one wanted to set up a country using the Mosaic Law as the law of the land, I should think that slavery as defined in the OT would be justifiable, though not the best. But as it stands today, no, you would not be justified in owning a slave.