Abraham Lincoln's notes for a debate

In these notes, believed to have been jotted down in preparation for a political debate, Abraham Lincoln (1809–1865) logically refutes the arguments that were being made in favor of slavery. After exploring the question, Lincoln comes to the conclusion that no one has the right to enslave another. 

"If A can prove, however conclusively, that he may, of right, enslave B, why may not B snatch the same argument and prove equally that he may enslave A?

You say A is white, and B is black. It is color then; the lighter, having the right to enslave the darker? Take care. By this rule, you are to be slave to the first man you meet with a fairer skin than your own.

You do not mean color exactly? You mean the white are intellectually the superior of the blacks; and therefore have the right to enslave them? take care again. By this rule, you are to be slave to the first man you meet with an intellect superior to your own.

But, say you, it is a question of interest; and, if you can make it your interest, you have the right to enslave another. Very well. And if he can make it his interest, he has the right to enslave you."