Were atheists involved in movements advocating the abolition of slavery serving as witnesses of Christ, witnesses of the gospel of Jesus Christ? No, of course not.Would he have had the Christians not being involved in abolishing Slavery movement, as that would be "worldly?"
I am saying that the Christian who sought political means to end slavery was being unfaithful and this unfaithfulness ultimately contributed to the failure of the churches in the civil right's movements.
Churches should have stood out against slavery. Churches should have stood out against racism. Churches should have stood out against social oppression. Unfortunately, Christians chose to abandon the Church and flee to politics to effect a desired end. And this has been one of American Christianity's largest failures as it replaced the gospel of Jesus Christ in many churches with political social justice.