In regard to the first point, the inferiority of the enslaved race. We may concede it is a matter of fact that it is inferior, but does it follow, therefore, that it is right to enslave a man simply because he is inferior? This, to me, is a most abhorrent doctrine. It would place the weak everywhere at the mercy of the strong. It would place the poor at the mercy of the rich. It would place those who are deficient in intellect at the mercy of those that are gifted in mental endowment.
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)