The arguments of the South on the topic of slavery were, as it turns out, somewhat scanty. They claimed to be taking a "literal reading" of the Bible, but one has to wonder. The first and foremost argument on slavery in the South comes from Genesis (Gen 9:20-27). It's the section after the Flood when Noah got drunk and Ham found him uncovered and passed out. Instead of covering him, Ham ran to tell his brothers. For his failure to respect his father, Noah cursed Ham. "Cursed be Canaan; a servant of servants shall he be to his brothers." (Gen 9:25) Well, there you have it, proof that it was not only justified, but moral for white people to enslave black people. Oh, wait ... did I miss something? How is that a "literal reading" of the Bible? For reasons inexplicable to me, the descendants of Ham (Canaan) were assumed to be the African races. (I don't suppose it matters that the tribes of Canaan were actually in the land of Israel (Gen 10:19).)1
Just as frequently used was the passage in Leviticus about buying slaves.
As for your male and female slaves whom you may have: you may buy male and female slaves from among the nations that are around you. You may also buy from among the strangers who sojourn with you and their clans that are with you, who have been born in your land, and they may be your property. (Lev 25:44-45)First, let it be recognized that God gave a specific command that kidnapping for the purpose of slavery was forbidden (Exo 21:16). I think we all know that the slaves in use in the South weren't "bought" but were exclusively kidnapped. Thus, forced slavery was a direct violation of God's commands (you know ... taking the Bible literally). In fact, kidnapping an Israelite for the purpose of slavery was punishable by death (Deut 24:7). And killing a slave had penalties (Exo 21:20). So if it is not forced slavery in view here, what is it? Well, God's laws included the possibility of what I'll term "self-slavery". The idea was that it was allowable for someone to sell himself into slavery. For Hebrews, it was with the understanding that there was a 6-year limit, although at the end of that time the bondslave had the option of choosing to make it permanent (Exo 21:1-6). In the text above the command is in regard to "the nations that are around you" and "the strangers who sojourn with you". So in what sense are we talking about Africans, and on what basis did this provide for the direct violation of God's command not to kidnap people for slaves? You know ... taking the Bible in a literal sense?
They also liked to point to Paul's letter to Philemon in which he returned Philemon's slave, Onesimus. "There, see? Paul was opposed to fugitive slaves." In fact, they used all the references to "slaves" or "servants" or "manservant" or "maidservant" as proof that it was biblical, justified, and even moral to kidnap people from Africa and force them into slavery in America. And, look, if you count all of those, clearly there are more than 6 references that "justify slavery", unlike homosexual behavior with only 6.
Now, some may argue that the case was settled and very clearly the Bible defends the right of the South to steal people from their lands and make them slaves. I will be candid; I don't see it. In fact, I think the argument is insane. But the question is not the sanity of the pro-slavery argument. The question is, is it the same thing as the argument that the Bible condemns homosexual behavior? Is it likely that Christians 50 years from now will look at their Bibles and the arguments of those of us who can read them and say, "What in the world were they thinking? It is an insane argument to claim that the Bible condemns homosexual behavior." How are these arguments different?
First, it should be abundantly clear that one is "permission" and the other is "prohibition". That is, there is no command in Scripture anywhere at all requiring slaves be taken, either by force or voluntarily. The argument for slavery, then, is a permission, not a command. The same it not true for homosexual behavior. All of the mentions of that behavior in Scripture are negative -- direct prohibitions. Simply put, the pro-slavery argument says, "This behavior (taking slaves) is permissible" and the argument against homosexual behavior says "This behavior is not permissible." If the pro-slavery argument can be taken at face value as valid, it must be taken as "allowed" and not commanded. That is, it is possible in some sense that some version of voluntary servitude might be found to be tolerated in the Old Testament, just as is polygamy and divorce, it is clearly not commanded (and forced slavery is forbidden). The same is not true for homosexual behavior. It is nowhere tolerated and all commands on the topic are a complete prohibition.
Second, if it could be argued from the Old Testament that kidnapping people to be slaves was acceptable (in direct violation of God's commands to the contrary), the New Testament addresses it. "Here there is not Greek and Jew, circumcised and uncircumcised, barbarian, Scythian, slave, free; but Christ is all, and in all." (Col 3:11) Paul told bondservants that if they could gain their freedom, they should (1 Cor 7:21). The New Testament suggests a change, then, whatever the Old Testament allowed. On the subject of homosexual behavior, this is not true. Both in the Old and New Testaments all references to homosexual behavior are universally negative. No hint of shift or change. No modification. All present a standard view that the behavior is sin.
Many argue that the biblical argument that marriage is the union of a man and a woman is just like the mistaken prohibition against racial intermarriage. It's not. You don't choose your race; you do choose your sexual behavior. And some argue that the biblical prohibition against homosexual behavior is the same as the mistaken defense of slavery in the South. It's not. There is no biblical command to take slaves; the Bible does proscribe homosexual behavior. The Old Testament may allow a version of slavery not at all like the American slavery of the 18th and 19th century, but the New Testament changes that. The Scriptures limit slavery in general (keeping in mind that it is not the same slavery as what we think of) and prohibit the American form of kidnapping for slavery; the Scriptures universally condemn homosexual behavior as sin. Finally, slavery was not historically defended by the church, but the church has always understood homosexual behavior to be sin. The question, then: Are these two the same types of questions? No. So why would we assume that God changed His mind? No reason.
1 There is another popular argument that I have to dismiss out of hand from Genesis. The argument goes that the mark of Cain (Gen 4:15) was that he was made into the first black man. Pulling that out of the text is impossible, except for the fact that Cain did have a mark. But the case falls apart immediately afterward when we read that in the Flood "Everything on the dry land in whose nostrils was the breath of life died" (Gen 7:23) with the sole exception of Noah and his family. Since everyone on the planet today is a descendant of Noah and his three sons (Gen 9:18-19), any remnant of Cain is ruled out entirely and the argument from the mark of Cain dies of drowning.