In 1965, Daniel Patrick Moynihan had this to say about American Christianity and slavery.

“The most perplexing question about American slavery, which has never been altogether explained, and which indeed most Americans hardly know exists, has been stated by Nathan Glazer as follows: “Why was American slavery the most awful the world has ever known?” The only thing that can be said with certainty is that this is true: It was."

"American slavery was profoundly different from, and in its lasting effects on individuals and their children, indescribably worse than, any recorded servitude, ancient or modern."

"In Brazil, the slave had many more rights than in the United States: He could legally marry, he could, indeed had to, be baptized and become a member of the Catholic Church, his family could not be broken up for sale, and he had many days on which he could either rest or earn money to buy his freedom. The Government encouraged manumission, and the freedom of infants could often be purchased for a small sum at the baptismal font. In short: the Brazilian slave knew he was a man, and that he differed in degree, not in kind, from his master.”

"[In the United States,] the slave was totally removed from the protection of organized society (compare the elaborate provisions for the protection of slaves in the Bible), his existence as a human being was given no recognition by any religious or secular agency, he was totally ignorant of and completely cut off from his past, and he was offered absolutely no hope for the future. His children could be sold, his marriage was not recognized, his wife could be violated or sold (there was something comic about calling the woman with whom the master permitted him to live a ‘wife’), and he could also be subject, without redress, to frightful barbarities—there were presumably as many sadists among slaveowners, men and women, as there are in other groups. The slave could not, by law, be taught to read or write; he could not practice any religion without the permission of his master, and could never meet with his fellows, for religious or any other purposes, except in the presence of a white; and finally, if a master wished to free him, every legal obstacle was used to thwart such action. This was not what slavery meant in the ancient world, in medieval and early modern Europe, or in Brazil and the West Indies."

The last sentence merits repeating a thousand times.