On slavery in the old testament and new testament: "Why did God permit slavery?" (from Piper)
Also, this from R.C. Sproul:
Slavery was an intimate part of the social order back then, and any perceived threat to the practice was seen as a threat to society. Throughout the New Testament we find the apostles willing to live at peace with this order for the sake of the gospel insofar as doing so did not compromise the gospel (for example, 1 Peter 2:18). For slaves this meant honoring their masters, as honor is owed to those God has placed in authority (Rom. 13:1–7; 1 Peter 2:13–14). Paul was not concerned with overturning slavery itself, and it should be noted that slavery in the ancient Roman Empire was closer to the modern-day employer-employee relationship, not the slavery of other eras based on kidnapping and racism, which Scripture abhors (Ex. 21:16; Gal. 3:28). In any case, to dishonor our supervisors today, as with a slave’s dishonoring of his master in the first century, falsely depicts Christianity, “as if God, whom we worship, incited us to rebellion, and as if the gospel rendered obstinate and disobedient those who ought to be subject to others” (John Calvin).Though the apostle did not argue against slavery, his teaching in 1 Timothy 6:2a was unheard of in his day. In ancient Rome, slaves obviously had a lower social status. Yet Paul says a slave’s work benefits his master, making him equal to him in the good he can do. Passages like this eventually led certain men in the West to fight for the abolition of slavery, and the gospel’s absence in other parts of the world may help explain why some nations still practice slavery today.Maybe the most amazing thing about slavery is that the Bible teaches that it is a metaphor of the Christian's relationship to Christ -- that Christ is his master. And what freedom comes with being a slave of the most good and perfect master!
But Moses was there, and wrote it all down plainly for us, but you reject what he says. If somebody rose from the dead to explain this to you, you'd reject him as well, because you don't want to believe it.
That explanation doesn't wash. If what is downright wrong is accepted because that is how society thinks at one point, (like homophobia, anti-abortion,lack of population control, or crooks who can afford to manipulate whole countries, or the obliteration of hundreds of earthly species because humans are special, attitudes prevalent today) is not objected to but condoned, because "god" supposedly condones such behaviour, then that religion, philosophy or notion should be condemned.