@Randy Kluth
Not *biblical* change.
Absolutely not. That is why the Bible Only people are stuck.
But the bottom line is....what is it that you want to do and still call yourself a christian?
Well, if I consult my wife, she would frown on my indulging in concubinage. ;) If I was to consult African Americans they would frown on my idea of owning slaves. But between you and me, these things are still legal by biblical standards, but not by State standards--I don't know about concubinage. The State has gotten very non-Christian and lax, morally.
As I said, conditions change, and the usefulness of these institutions become questionable in either a Christian or a post-Christian society. They had their day, and yes--things changed. But the Bible didn't change, nor has Christian morality. Social standards do change, and we are encouraged, in the Bible, to show respect for our State and its laws.
As a Christian I view such things as Slavery and Concubinage as unnecessary and undesirable, with respect to the Gospel testimony. We want to bring people to the Lord and to be just towards all. That is a more complicated formula than you seem to want to make it.