I've been studying several books on the history of slavery in the USA including:
Fit for Freedom, Not Friendship (2009)
The Origins of Pro-Slavery Christianity (2008)
Slavery and the Meetinghouse (2007)
On my Kindle / smartphone / laptop:
The Civil War as a Theological Crisis (2006)
Quaker neoliberals of the pre Civil War period were quasi-uniform in condemning slavery but not in a "right now, get rid of your slaves" sense. Government had legitimized slaves and the rights of slave owners should be protected against religious zealots who might impose other forms of zealotry once given the reigns of power. Quietists don't trust the shrill. Plus the immigrant pioneer settlers had a similar solution for all social ills: send the troublemakers elsewhere. Recruitment into evangelist churches had much to do with preparing slaves for God's plan to send them to Haiti and Liberia. Quakers who couldn't abide slavery moved west and north.
Slaves tended to embrace Christianity for its promise of Liberation, ala the later Catholic Liberation Theology of Central and South America. The non-slave class needed countering pro-slavery arguments to bolster Christianity as a slavery-justifying religion. As the Bible is but clay in the hands of a skilled minister, it comes as no surprise that both pro- and anti-slavery extremists sought comforting words from this book. This has continued to be the way to win friends and influence people in North America: thump the Bible like a drum, but with a characteristic beat pattern that attracts your own kind (anti-gay, white-supremacist or neoliberal or whatever).
Many settled, well off Quakers did not like the "immediatist" position, whether they held slaves or no. In social theory, slaves should be free, but until a new homeland could be found in Africa or someplace, some "Israel" (a promised land), they'd have to put up with 2nd class treatment as guests in this New World.
True, the slavers felt a different kind of relationship to the slaves than to the native peoples (Pueblo). The pueblo had not been "invited" as in forcibly removed from their homeland and brought to America by boat. Anglo-Euros and Africans were both here as boat peoples. The Christians put a lot of pressure on themselves to "convert" their guests, so they would "think as we do". Interracial church services were the norm in many counties of Virginia, as slaves were encouraged to take in the English view of themselves. The Pueblo, on the other hand (I'm using the term inclusively, not just for the folks near the Rio Grande), were going to be a more classic enemy to be fought with weapons. "If they won't join you, beat 'em" was the rallying cry.
The Quakers mostly disagreed with this philosophy and were ostracized as "people lovers" i.e. "lovers of human beings". Their "no human being is illegal" campaign typifies their belief in a universal Inner Light, whereas most North Americans have a knee-jerk impulse to criminalize the undocumented and oppressed as a source of cheap prison labor (slavery is still going strong in the USA, by these other labels (one might argue the South won)).