"If certain Christians like slavery, and slavery is wrong, then Christians like what is wrong.
Because Christians like what is wrong, and Christians like the Bible, then the Bible is wrong."
Or is it?
"Most Christians of the old South thought slavery was a pretty good idea."
I don't have any information to judge the percentage of old South Christians that liked slavery. But I can see that if slavery was in their temporal and financial advantage to maintain, that would be quite a slant with which to come to the table of biblical interpretation.
"Weren't a number of prominent abolitionists freethinkers?"
As for abolitionists of note, William Wilberforce - a strong Christian - has always figured most prominently in my studies, along with a great many Quakers. There might have been a number of freethinkers on board as well (anti-slaverysociety.addr.com).
Isn't one interpretation just as good as the next?
What is "Christian"?