The Gospel of Slavery: A Primer of Freedom, written by a Unitarian minister and published in Philadelphia in 1864. More information at Slate's new history blog, The Vault.
This argument, interestingly, that faith was undermined by contorted arguments about slavery, was often made by the other side, by those supporting the positive good of the institution of slavery. Christian abolitionists were regularly condemned for not reading the Bible literally, and betraying true, orthodox Christianity in their (radical) attempts to abolish slavery. One standard argument, from the South, was that the pro-slavery forces were actually preserving Christianity against the corruptions of those who had been influenced by rationalists, atheists, and so on.
It was the case, after all, that "Revivals of religion and revivals of the slave-trade go hand in hand together."
The prominent presence of non-traditional Christians and even non-Christians, such as this
As one Confederate famously argued, the armed defense of slavery was a defense against the evils of revolutionary atheism:
For 'Liberty Equality, Fraternity,' we have deliberately substituted Slavery, Subordination and Government. Those social and political problems which rack and torture modern society we have undertaken to solve for ourselves, in our own way, and upon our own principles. That among equals equality is right;' among those who are naturally unequal, equality is chaos; that there are slave races born to serve, master races born to govern. Such are the fundamental principles which we inherit from the ancient world, which we lifted up in the face of perverse generation that has forgotten the wisdom of its fathers: by those principles we live and in their defence we have shown ourselves ready to die. Reverently we feel that our Confederacy is a God sent missionary to the nations, with great truths to preach.It's exactly in this context that Frederick Douglass argued that there were two types of Christianity in America, the severity of the split between them being such that, as historian Mark Noll argues, the American Civil War actually began within the internal divisions of American Christianity.