"In all the ages the Roman Church has owned slaves, bought and sold slaves, authorized and encouraged her children to trade in them. Long after some Christian peoples had freed their slaves the Church still held on to hers. If any could know, to absolute certainty, that all this was right, and according to God’s will and desire, surely it was she, since she was God’s specially appointed representative in the earth and sole authorized and infallible expounder of his Bible. There were the texts; there was no mistaking their meaning; she was right, she was doing in this thing what the Bible had mapped out for her to do. So unassailable was her position that in all the centuries she had no word to say against human slavery. Yet now at last, in our immediate day, we hear a Pope saying slave trading is wrong, and we see him sending an expedition to Africa to stop it. The texts remain: it is the practice that has changed. Why? Because the world has corrected the Bible. The Church never corrects it; and also never fails to drop in at the tail of the procession — and take the credit of the correction. As she will presently do in this instance."

— Mark Twain

We have discarded slavery because we have finally decided to take Paul at his word, when he tells us that “in Christ, there is neither Jew nor Greek, slave nor free, male nor female, for you are all one in Christ Jesus.”  We’ve decided, in other words, that despite the countenancing of slavery in other biblical texts (including other texts attributed to Paul himself), the very heart and soul of the gospel is summed up in Paul’s proclamation of the freedom and equality of all believers in Christ.
We’ve decided that the bible was not really ever about—not in its most essential proclamation about who God is and what God desires for the world—the subordination of one group of people to another, the subjugation of one group of people by another.  It’s about, instead, a vision of a world in which every one who comes from the hand of God is treated with equal dignity and respect.  And has equal access to the goods of the world.  And to the rights accorded to everyone merely because she is a human being.
We have long since gotten this when it comes to the issue of slavery.  Why, I wonder, is it taking the Mr. Smiths of the world so long to get it when it comes to the issue of gender roles, and the power allocated to men and to women respectively?  And to the related issue of sexual orientation?
-William D. Lindsey