I was recently made aware of a debate going on in the neo-reformed Gospel Coalition corner of the world that I tend to avoid. Doug Wilson, a pastor from Moscow, Idaho, argued in his book "Black and Tan" that the abolitionist movement was wrong and the Civil War should never happened, because if Southern slave-owners had been allowed to implement the Bible's teachings on slavery, then a more humane transition would have taken place through "gospel gradualism." This spring, a Caribbean neo-reformed pastor, Thabiti Anyabwile, who writes for the Gospel Coalition, decided to take up the issue and engage Wilson in a debate which has been summarized in this piece I encountered on the Wartburg Watch blog.
I'm of course horrified that this conversation is happening at all, but I'm going to try to represent Wilson's view as accurately as possible so that I can't be accused of caricature. Basically Wilson seems to be coming at this from several angles which I would summarize in the following three points based on direct quotes taken from his blog and Anyabwile's blog:
1. If we say that Christians can't fight a civil war today to stop abortion from happening, then we shouldn't say that the Civil War were justified as a means of freeing slaves.
"If we could bring an end to abortion in the United States by precipitating a war (or by trying to), should we do that? Abortion is at least as great an evil as slavery was. Abortion is at least as great an evil for black culture as slavery was. If you allow for gospel gradualism now, then why is my urging a gospel gradualism in 1858 a thought crime? And if gospel gradualism was sinful then, why isn't it sinful now?" 
2. "Liberal" Christians have used the Bible's endorsement of slavery as a means to dislodge their obedience to the Bible's teachings on female submission to their husbands and homosexuality, so if Christians are going to hold onto the "biblical" view of marriage, then we have to be pro-slavery as long as it occurs in biblical terms.
"Christians must live or die by the Scriptures, as they stand. Compromise on what the Bible teaches about slavery is directly related to the current pressures to compromise on abortion and sodomy. Southern slavery was an example of the kind of sinful human situation that called for diligent obedience to St. Paul's directives, on the part of both masters and slaves. Because this did not happen, and because of the way slavery ended, the federal government acquired the power to impose things on the states that it did not have before. Therefore, for all these reasons, radicalism is to be rejected by Christians." 
3. If Southern whites had been allowed to gradually grow out of slavery on their own through the Christian teaching of their pastors rather than having emancipation forced on them by the federal government, then we would have a better balance of power between state and federal governments today.
"The discipleship of the nations is a process. This means that the South was (along with all other nations) in transition from a state of pagan autonomy to one of full submission to the Lordship of Christ. Christian influence in the South was considerable and extensive, but the laws of the South still fell short of the biblical pattern. In spite of this, the Christian influence on antebellum Southern culture surpassed most other nations in the world of that time." 
Well, at least Wilson concedes that the South "fell short of the Biblical pattern." I don't think I've ever seen more white privilege and presumptuousness packed into a sentence than that one.
The Real Issue: Is the Bible Culturally Contextual?
So here's the hard truth. Wilson has made a choice to be consistent in his view of the Bible as a document whose teaching is absent of any cultural context. The biblical inerrantist position requires holding that what the Bible says to first century Jews and Gentiles must be implemented in exactly the same way today and not translated into a different contextual form.
If Paul says for ladies to wear hats in church, then they need to do that today even if uncovered hair had a different, explicitly erotic meaning in Roman culture that it doesn't have today. If you allow context to be part of your biblical interpretation, then you're sliding down the slippery slope into liberalism. As Wilson says: "Compromise on what the Bible teaches about slavery is directly related to the current pressures to compromise on abortion and sodomy."
I actually commend Wilson for his consistency. Most biblical fundamentalists pick and choose where to be literalists. I myself read the Bible contextually. The early church had to operate within a first century Roman culture shaped by a specific set of assumptions about slavery and gender. They had to decide which battles to fight and which times to choose martyrdom as a means of fighting. It doesn't matter whether Roman slavery was "more humane" than American slavery. The Roman paterfamilias had absolute life and death power over his household, period.
To me, it is reasonable to look for the spirit behind the teachings that are given in order to translate those teachings into a different cultural context. This requires paying attention to the only verse in the Bible that the inerrantists don't consider infallible: "The letter kills but the spirit gives life" (2 Corinthians 3:6). I don't think that women need to wear hats to church today, but it does seem reasonable to hope that men and women alike would not wear clothing to church that features their assets in a way that is deliberately provocative and distracting.
Likewise, we don't have to conclude Peter and Paul are teaching us that slavery is right even when they say, "Slaves, obey your masters." They are calling on slaves to act in such a way that will most likely convert their masters to Christ. It's the subversive evangelistic goal which is the relevant teaching that can be translated into our context; we should see relationships with our bosses as opportunities for evangelism through the witness of faithful hard work.
Because of my contextual view of Scripture, it doesn't bother me to say that we do not have to operate today with either first century presumptions about slavery or the first century account of gender as a simple black-and-white binary. Doug Wilson's fear is well-founded. I believe that God did in fact use our discovery (18 and a half centuries too late) that we must follow the spirit rather than the letter of what the Bible says about slavery as a means of opening up a culturally contextual way of accessing the real truth of His scriptural teachings.
With regard to gender, we've discovered that people are not simply male or female. Some people are born with both organs; others are born with a male organ and female hormones and vice-versa; others are born with a combination of hormones that make a lifelong relationship with others who share the same gendered organs the least disruptive arrangement for them to have a fruitful journey of Christian discipleship. The best I can do in capturing the spirit of biblical teaching on sexuality is to say that Christians should promote a form of chaste sexuality for all people gay and straight, which best resists its dangerous tendency toward idolatry (which is the real issue, not some artificially constructed order of gender that gets superimposed on top of the Bible by those who do not allow cultural context to be part of their interpretation). That means as Paul says, that it is "better to marry than to burn" (1 Corinthians 7:9) even though Paul thinks celibacy is ideal for gay and straight people alike (1 Corinthians 7:7).
I think that Doug Wilson's perspective and mine represent the two basic possible choices for how to approach biblical interpretation if you're going to do it consistently: with context or without context. Many Christians choose a inconsistent path in between based on whatever ideological identity they're staking out with their mixture of positions. My fellow Methodists are the most hypocritical group because they want to have female pastors, which are explicitly forbidden in the Bible (if read without context), but oppose homosexuality, when the biblical opposition to homosexuality stands or falls on the question of whether Paul's first century assumptions about gender are permanently normative and essential to his divinely inspired teaching.
If you're not willing to consider whether Paul's take on gender hierarchy and homosexuality might both occur within a set of assumptions about gender that are not permanently part of God's plan for humanity, then you need to go along with Doug Wilson and say that slavery is OK as long as it occurs in a biblical way because Paul has to be right about that also. If you want to learn how to own slaves in a biblical way, then you can check out 19th century Methodist pastor Holland Nimmons McTyeire's "Duties of Christian Masters."