Number five is partly true and partly false. Slavery was very profitable for those plantations that were large enough to employ the gang system. Technology would have changed that though and would have done so a lot sooner if the war had not destroyed Southern investment capital and broken up the large plantations. European pressure was also building and would have push the South towards abolition. The British in particular were becoming increasingly fanatical about it. But the biggest reason the South could not have survived as a slave society has to do with the cost of dealing with fugitive slaves. With the north no longer constitutionally obliged to return runaway slaves the South could not have afforded to maintain a slave economy. There have only been five examples in history of societies that built their entire economies on slave labor: the Greeks, the Romans, the Caribbean Islands, Brazil, and Dixie. The one thing they all had in common was the ability to socialize the cost of runaway slave management. In every case except Dixie the slave economy ended when this advantage disappeared. In the case of Brazil this was particularly dramatic. One province abolished slavery, runaway slaves began flocking there, and the economies of all the other provinces collapsed. The large slave owners then began calling for abolition as a means of encouraging workers to stay and work.
"Vindicating Lincoln: Defending the Politics of Our Greatest President" by Thomas L. Krannawitter