The justification of slavery is placed, so far as I know, mainly upon these grounds. The inferiority of the enslaved race, the fact that enslaving men imparts Christianity and civilization to them, and thirdly, the guarantees of the Constitution. These are the three main arguments presented to justify slavery, and consequently to justify its expansion, and by the way, I hold that the extreme men, as they are called, on this question, are the only men who have the logic of it. I am right or the fire-eaters or right. If slavery is right in Virginia, it is right in Kansas. If it is wrong in Kansas, it is wrong everywhere.

As quoted in His Brother's Blood: Speeches and Writings, 1838–64 (2004), edited by William Frederick Moore and Jane Ann Moore, p. 193 - Speech to the U.S. House of Representatives (April 1860)