In the 19th century you could not be for slavery and racial equality at the same time. Harriet Beecher Stowe did not write UTC to advocate racial equality in the secular and social sphere. She wanted to end slavery, which opposed her notions of Christian morality. Slavery had to be abolished for the nation to be purified of its national sin. But in neither of these arenas did anyone question the assumption of a racial hierarchy.
Racial differences are innate.
There must have been separate and unequal creations. The American school of ethnology affirmed on the basis of cranial measurements and other archaeological evidence that blacks were permanently inferior to whites. This theory allowed for slavery, Indian extermination, and imperial expansion. Racial differences are the product of environment. This theory relies upon the assumption that a race can literally be transformed through the power of the environment.