In Brooks' novel March, why do Southerners who support slavery not want slaves to learn how to read and write?

Brooks'
novel reflects the Southern reality regarding the education of slaves.  There is little doubt
that some of the slaveowners were simply cruel, regarding their slaves as objects or non-
humans.  In this light, it would simply make no sense to spend the time or the effort in
teaching an object how to read or write.  At the same time, these slaveowners were convinced
that slaves were not human.  In teaching them to read and write, there is a human connection
present which would undermine many of these slaveowners' construction of how slaves were
seen.

However, some Southerners simply lived with the contradiction of
seeking benevolence,...