If you don't know about Ed Brayton, he has one of the most interesting blogs on the net. He is a Panda's Thumb contributor (and therefore virulently anti-ID) and a non-believer, but his writing and his reasoning skills set him apart from the rest of the PT crowd. I almost never agree with him, but I enjoy how his mind works, and he often surprises me.
Today he has a thread on Slavery and the Bible which is more or less dedicated to me.
You'll find my comments sprinkled throughout. The gist of my argument is this: Although slavery is not explicitly condemned in the New Testament, and even though Paul sent Onesimus back to Philemon, that in no way implies that God condones the institution of slavery or that slave-owners will escape judgment. Paul sent Onesimus back to (a) obey the law and (b) to spread the Gospel.
Jesus did not come with a social gospel promising personal liberty and justice for all men in this life. (In fact, he promised suffering.) He came with a gospel offering eternal life to the faithful, and Onesimus (gladly, I suspect, although it’s just a hunch) returned to Philemon ready to bear witness to its power. That does not make slavery or Philemon right, it simply shows what Paul thought was important.
Paul's life is a testimony to: preach the gospel regardless of your situation; anything else is the tail wagging the dog.
UPDATE: Eric Seymour of In The Agora jumps into the fray.