In fact, slaveholders had no problem with Jesus admonition because they did not consider slaves as their "neighbor," and therefore they saw no contradiction. Slaves were property, and as property, belonged to their owner;neighbors belonged to no one. More importantly, throughout the Old and New Testaments, slavery is never treated as an ill; in fact slaves were commonplace. Jesus himself never spoke against it. In the New Testament (Philemon) Paul sends a slave back to his master.
Defenders of slavery often quoted from Genesis in which Noah cursed his son Ham. Ham was the father of Canaan:
And Ham, the father of Canaan, saw the nakedness of his father, and told his two brothers outside.Then Shem and Japheth took a garment, laid it upon both their shoulders, and walked backward and covered the nakedness of their father; their faces were turned away, and they did not see their father's nakedness. When Noah awoke from his wine and knew what his youngest son had done to him, he said, "Cursed be Canaan; a slave of slaves shall he be to his brothers.
Rev. Josiah Priest in a lengthy treatise defended slavery on Biblical grounds:
Convince tlie slaveholder that this relation is incompatible with Christianity and republicanism — he stands ready to abandon it, regardless of the sacrifice. His mind is not sealed against the impressive teaching of truth and reason, nor his heart seared against the moving influences of pure benevolence and true Christian charity. But, hitherto, the agitation of this question has been altogether one-sided, and confines mainly to those in whose action upon this subject, neither right, reason, nor justice, were involved.
In sum, slaveholders saw no contradiction between Jesus command to love one's neighbor and slavery, as slaves were not one's neighbor.
Slaveowners were able to tell themselves that holding slaves was not incompatible with loving their neighbors. There were two major approaches to this.
First, they could tell themselves that blacks were inferior and "loving" them did not involve treating them as equals. Men "loved" their wives and children but did not treat them as equals. Therefore, enslaving blacks was not inconsistent with loving them. It was loving to treat people according to their appropriate place in the world.
Second, they could tell themselves that they did not treat slaves all that badly. They could argue that they treated their slaves better than workers in Northern factories were treated. This, too, would be consistent with treating the slaves in a loving way.
The slave owners, then, felt that they were treating their slaves in ways that were completely appropriate.