What argument was used by southern slaveholders to justify slave labor?

There were three types of arguments: a theological one, claiming that The Bible called Blacks "choppers of wood and carriers of water" (quoted from memory); a pseudo-humanitarian one, that Blacks were incapable of managing for themselves; and a pragmatic one, that the economic well-being of [white] society depended on the free labor of slaves. Altho it may sound unbelievable that people were not ashamed to use the last of these arguments, it is not that different from what I heard on the radio yesterday, someone arguing against the Health Care reform because giving health care to more people would raise his insurance premiums.