Its all Great, but feelings and you accept the fact they they can chose to do so.. Wich they con not. In real life, they used to give much to the soundhen economy.. And did not get hiret when they where freed ether.. but mostly staved and shit..
Slaves can and could choose.
When you read up for more than a casual glance you happen upon a lot more than 'work to the bone and nothing else'.
Independent culture, independent income (yes, slaves could have savings), limited rule of law (as in: There are certain penalties that are established and accepted. Should one overseer overstep these he might find himself the only white man among a very hostile population of 500 blacks who have ways of killing him without condemning themselves), etc.
There is also the fact that a person who is told to work and forced will hardly ever be as productive as a person exploiting him/herself for his/her own gain, children ,etc.
It is true, they did give much to southern economy, especially low wage labor force that could not migrate, sparing the plantation owners the hassle of competing with the North for the workforce, but then again today there a still large agricultural complexes in the US requiring large, low wage workforces. They just use illegal aliens from Latin America these days.
Slavery works, as does Serfdom.
Nobody doubts that.
But if your industry is putting out large quantities of cheap goods you need somebody to buy them.
If your workforce is unable to earn money (therefore unable to spend money) you lack a marketplace for these goods.