And yet, as already quoted, the Vice President of the Confederacy gave a speech glorifying the formation of a new state, based in a slave economy and the notion that slaves were inferior beings. So all of the theorizing is essentially psuedo-intellectual clap trap because the people who were seeking to secede from the Union were very clear about why they were doing it. Also, whether or not the emancipation proclamation was constitutional is entirely ancillary to this question.
As already pointed out, we do still have what is essentially slave labor in many agricultural settings, and have ever since formal slavery was abolished. Because it is still an economically viable construct.