There is a natural disgust in the minds of nearly all white people to the idea of indiscriminate amalgamation of the white and black races... A separation of the races is the only perfect preventive of amalgamation, but as an immediate separation is impossible, the next best thing is to keep them apart where they are not already together. If white and black people never get together in Kansas, they will never mix blood in Kansas...
The Writings of Abraham Lincoln, Including the Full Text of the Lincoln-Douglas Debates Together with the Essay on Lincoln (ed. 1905)