Which branch of Christianity though? There was a huge disparity in approaches in new england colonies (ie rhode island thought the indigenous should have rights, Massachusetts couldn't give a shit about anyone other than the elected.)
A lot of the english abolitionists were radicals, well outside the mainstream. The Quakers, Methodists, shakers were all deeply scary to the establishment
The US has tended towards justifying slavery, and its arguments included the ¨curse of Ham" borrowed from Muslim slave traders. British colonies in the Caribbean produced censored version of the Bible for slaves.
You mean the books of the Bible containing rules explicitly rejected by Christians from the start? The rules that Jesus is recorded as saying was a moral compromise? You are also conveniently skipping over the declarations of equality (with regard to slavery, race and sex) in the New Testament.