That seems a bit disengenuous . There were poor immigrants who worked in the South for low wages as well. No capitalist nation didn't use low paid labor and often used low paid immigrants.Confederacy imposed Tariffs. Those revenues stayed in the Confederacy. Most assuredly, the inflated price paid for Yankee Manufactured Goods, did not.
So, if you wanted to expand your economy, might you want to manufacture your own goods, collect your own taxes? Many Fire Eaters thought so. Slavery was a labor solution. Just like importing poor immigrants and paying them starvation wages. Neither is an economy.