Okay, this post at JohnShore.com led to a whopping 560(!) replies before meltdown occurred, which forced Don M. Burrows to post this summation of one sub-argument on his Nota Bene blog since he couldn't respond directly. Don torpedoes a claim made by a poster on the JohnShore.com thread that New Testament era slavery was significantly different from what we in the 21st understand slavery to mean (it was somewhat different, but only in the details).
Where Don pings on my radar screen is when he writes "the approval of slavery [is] explicit in much of the New Testament".
The Bible, both OT & NT but in particular the OT, is pretty explicitly down on slavery, certainly as a permanent condition.
The law of Moses required indentured servants to be freed after 7 years of servitude (this probably reflects on a pre-Moses tradition, viz. Jacob voluntarily working for Laban for 14 years in order to marry his two daughters, Leah and Rachel).
That the ancient Hebrews and classical era Jews used various underhanded stratagems to circumvent this law is undisputable (again, harkening back to Jacob; he wanted only one of Laban's daughters but Laban pulled the old switcheroo on him, swapping out the older daughter Rachel for the younger daughter Laban whom Jacob desired, thus getting another 7 years worth of work out of him). In this they were no different from the founding fathers of America; they recognized slavery as an evil, they embraced the intellectual concept of all men being brothers, but still accepted/encouraged/protected the actual practice.
Nonetheless, in both the OT and the Declaration of Independence there is unmistakeable language to indicate slavery, even though it exists, is not and should not be a normal part of the human condition.
Likewise, in the NT it's pretty explicitly stated that God finds no difference between male & female, Jew & Gentile, slave & free. Christ repeatedly taught on being submissive to terrestrial authority (so long as it did not require a compromise of spiritual principles) & that the ideal life was one of servitude to others. A voluntary servitude, to be sure, but still servitude.
Paul also admonished slave owners to treat their slaves fairly & humanely (likewise he admonished parents to be kind to their children and husbands to their wives). Everybody in the Roman world knew the brutal reality of slavery; to say there was no difference between the owner and the slave was a radical conceptual leap.
So while Paul recognized the reality of the existing system & only tried to mitigate its worse aspects, not eradicate it entirely, nonetheless his epistles laid the groundwork for the eventual abolition of slavery.
Like divorce, slavery is tolerated but not condoned by scripture.
In any case, check out both John & Don's blogs; they're both pretty savvy, knowledgeable guys.