Ed Brayton's got some great posts on slavery and the Bible.
Money quote from the first post:
This is one of the primary reasons why I can no longer accept the Bible as the word of God, as I once did. It makes no sense that God could have found the time or interest to inspire men to pass on his commandments regarding the most mundane of things - whether to cut one's hair, whether to wear mixed fabrics, how to dress, and so forth - yet never does he bother to say "don't own slaves". And this even when he had the perfect opportunity to do so when the events regarding Philemon present themselves to Paul. If God was indeed inspiring Paul to write, why on earth would he not have Paul condemn slavery as contrary to the teachings of Christ? It simply makes no sense, nor do any of the apologetic rationalizations for it.
The second post deals with some attempted obfuscations on the part of apologists for the Bible. But as Brayton demonstrates, the Bible clearly endorses slavery -- the owing of people by other people -- at times. For instance: Leviticus 25: 44-46:
"Your male and female slaves are to come from the nations around you; from them you may buy slaves. You may also buy some of the temporary residents living among you and members of their clans born in your country, and they will become your property. You can will them to your children as inherited property and can make them slaves for life, but you must not rule over your fellow Israelites ruthlessly."
I, like Brayton, view this as proof of the Bible's moral errancy. Indeed, in this past post I noted "[o]n some of the most elementary issues of morality, the Bible, read [as a literal inerrant whole], falters." The post showed that certain parts of the Bible endorse both slavery and genocide, two of the most basic moral wrongs.
Finally, just let me state that I am not "judging" the Old Testament Jews, or even the longstanding practice of slavery in the Christian West. That tribe was just emerging out of a sub-barbaric evolutionary "state of nature" where might made right, and viewed in this context, the Ancient Jews were civilized for their time. Similarly, slavery is one of the oldest cross-cultural traditions, right next to the family. What is unique about Western Civilization was not that it started slavery, but that it ended slavery. And through the mechanism of "colonialization" and forcing "Western" values on non-Western lands, the West abolished slavery globally (at least in legal theory, if not in actual practice where slavery persists to this day).
However, the Christian practice of slavery and the moral content of the Bible is defensible only when viewed through an historical lens, where we don't "judge" the past by the moral standards of the present. However, that poses a problem for fundamentalists who claim that the Bible is inerrant and as True, Right and Just today as it was when written. Because judged by modern moral standards that view slavery and genocide as always wrong no matter what, when, where, or how practiced, the Bible clearly is morally errant.