I still see no ban on slavery in the Bible. It regulated slavery, and admittedly tried to make the life of the slave easier.
he become the first human being in the history of the world to speak out unequivocally against it (in his Letter to Coroticus) as being morally evil.
That is good. It is also long after the establishment of God's word.
As you imply, later Christians deeming slavery to be immoral is a re-interpretation of the Bible. But they did this according to the mores of the society of the time. Going back to find a supporting verse is simply justification for the decision.
Sometimes I think the Bible is poorly written because of the contradictions, etc. However, it would have been smart to put in all of the contradictions so that the interpretation of it could change with a growing society with an evolving set of mores, all with scriptural support. The better religious books tend to have all the bases covered.
I understand you objection, but I think you're expecting the Bible to be the Koran.
Please don't take this as an insult, but as a note about the nature of religious truth. Namely: you might find the Koran more to your liking, inasmuch as it is not "inspiration" but "recitation." (Koran means recitation.) The Koran has laws which are directly transcribed into Shari'a. This is possible in Islam because there is no necessary interaction between Allah's will and the human mind. It is not a dialog. It is a decree.
This is quite unlike the Bible, which was written in three languages (Aramaic, Hebrew and Greek) and three continents (Europe, Asia, and Africa) by some 80 different authors over a period of 800 years. Unlike Mohammad, these authors did NOT get possessed by a bodiless spirit and were NOT compelled to recite or write as dictated. What happened to them is a far more supple and interactive thing called "inspiration" --- which means they wrote consciously, in their own style, using their own words, drawing on the cultural vocabulary and images that were available to them int heir own experience.
The beauty of it is that what you have is not a dictator's monologue, but a dialogue of divine initiative and human response.
The Hebrew Scriptures were written in a society in which slavery, polygamy, concubinage, tribal vendetta, etc. were already present as a given. God's word in this context is not a blessing of the status quo, but an invitation to adveniat regnum tuum--- Thy kingdom come. A kingdom which is literally our task to work out.
You could say God supplies the inspiration, and we supply the perspiration.
God is not looking here for slaves. John 15:15
"No longer do I call you slaves, for the slave does not know what his master is doing; but I have called you friends, for all things that I have heard from My Father I have made known to you."
That means we have to work out all the implications based on a progressively fuller grasp of what God is up to!
Doesn't it strike you, the difference between Islam ("submission") and Israel ("wrestler with God")? Can't you see the progression between God saying in Exodus "Do not oppress people, for you yourselves were once slaves in Egypt," to St. Paul saying to Philemon "accept your manservant back, not as a slave but as a dear brother" and St. Patrick saying, "If he's your brother he can't be your slave"?
This is human response to a Word Who is always going before us. And we are the sons and citizens -- not the dhimmis--- of the kingdom.
Except for the fact that none of them have a Savior.
You get to 'be good' to get to 'heaven'.