This is actually why economics is called the "dismal science", it's not because everyone hates economists, a slave-owner gave it that name because he was mad economists didn't like slavery.
There's a reason why overall income didn't really go down in 2020 (and even increased in some places), and thats because poor people don't actually make that much money, nor do they provide any significant value.
I’d love to see this reasoning or study behind this, and the context of “poor people”.
As for literature backing this up, Adam Smith in Wealth of Nations talks in detail about slavery in the American colonies.
He gives examples where slavery was only viable in the southern states where they grew tobacco. Maybe one of the reasons why the South were so opposed to the end of slavery vs the North where slavery was expensive