It didn't take Christians to realize slavery was wrong, besides how can you prove a single person disagreed? Believing that killing and stealing are wrong goes back a lot further than Christianity.....
You're the one who brought up slavery, people in those states should have been able to work it out for themselves.
By the way, the priests being reassigned? That has been reported in the news and that can be proven by the fact a guy was at one church and then is suddenly transferred after the controversy. Maybe that hasn't come up in the UK, I don't know, but don't imply I'm making it up....