Why are members of the Creighton family so divided about the idea of secession from the Union?

Matt argues that the Southern river states will suffer if Kentucky wants to secede While Mat argues that, "separate, we're jest two weakened, puny pieces, each needin' the other." They they live in south indiana and that is supposed to be a union state but it is also close to the boarder so many of the families may have moved feom slave owning states to indiana.