“The Southern states would have had an economy that was substantially the same had there been no slaves. Its climate and soil were well suited to producing valuable cash crops. Those crops were going to get produced given the demand for them”
Have to disagree. In 1860 about 2 million slaves were directly involved with cotton agriculture. Without them, where would the 2 million white workers come from to replace the labor necessary to produce the 5.3 million bales of cotton that were produced that year. Without slaves, that would not have happened.
Suppose they had been sharecroppers instead - as they were after the war. Suppose they had been paid a wage. There were markets for those crops and those crops were valuable. They were going to get produced. If not Africans, then there were plenty of dirt poor Europeans who could have been brought over for periods of indenture (as was common in the early colonies) or for wages. They would have been able to offer a wage to attract the labor necessary to produce those crops.
Also, it should be noted that plenty of cash crops WERE actually produced by yeoman farmers and their families. It wasn't all large plantations. It was a standard practice to devote a portion of their land to growing cash crops to raise the money for all the things they could not produce themselves. Some entirely farmed cash crops because it was more profitable than subsistence farming.