Slavery, of course, is indefensible on moral grounds. But you can’t make a good economic case for it, either:
This notion that slavery somehow benefited the entire economy is a surprisingly common one and I want to briefly refute it. This is related to the ridiculously bad academic study (discussed here) that slave-harvested cotton accounted for nearly half of the US’s economic activity, when in fact the number was well under 10%. I assume that activists in support of reparations are using this argument to make the case that all Americans, not just slaveholders, benefited from slavery. But this simply is not the case.
At the end of the day, economies grow and become wealthier as labor and capital are employed more productively. Slavery does exactly the opposite.
Slaves are far less productive that free laborers. They have no incentive to do any more work than the absolute minimum to avoid punishment, and have zero incentive (and a number of disincentives) to use their brain to perform tasks more intelligently. So every slave is a potentially productive worker converted into an unproductive one. Thus, every dollar of capital invested in a slave was a dollar invested in reducing worker productivity.
Europe, whence came a heck of a lot of settlers, was a wholly different place:
As a bit of background, the US in the early 19th century had a resource profile opposite from the old country. In Europe, labor was over-abundant and land and resources like timber were scarce. In the US, land and resources were plentiful but labor was scarce. For landowners, it was really hard to get farm labor because everyone who came over here would quickly quit their job and headed out to the edge of settlement and grabbed some land to cultivate for themselves.
In this environment the market was sending pretty clear pricing signals — that it was simply not a good use of scarce labor resources to grow low margin crops on huge plantations requiring scores or hundreds of laborers. Slave-owners circumvented this pricing signal by finding workers they could force to work for free. Force was used to apply high-value labor to lower-value tasks. This does not create prosperity, it destroys it.
And when it was outlawed, it was replaced by something nearly as bad. Sharecropping earned little money for the workers, and did next to nothing for the Southern economy. Even those clueless Yankees could figure that out.