You're not wrong, it's the logical next step for capitalism.
"Again we have diluted ourselves into believing the myth that Capitalism grew and prospered out of the protestant ethic of hard work and sacrifice. The fact is that Capitalism was build on the exploitation and suffering of black slaves and continues to thrive on the exploitation of the poor – both black and white, both here and abroad. If Negroes and poor whites do not participate in the free flow of wealth within our economy, they will forever be poor, giving their energies, their talents and their limited funds to the consumer market but reaping few benefits and services in return." - Martin Luther King
Well MLK was a theologian, not an economist. Many countries have capitalism and never had slavery. And while they have a mindset that isn’t “Protestant work ethic,” it’s indistinguishable in relevant part. E.g. Singapore, Japan, South Korea, Taiwan, etc. https://twitter.com/dnystedt/status/1558863974883823617
> Many countries have capitalism and never had slavery
You ignored the second part of his statement, where he claimed that since slavery ended, capitalism has been propped up by the exploitation of the poor. Those countries may not have slaves but they do have poor people.
All countries have poor people. The capitalist ones have fewest of them, because capitalism makes poor people wealthier, unlike alternatives, which make them starve and die.
You're not wrong, it's the logical next step for capitalism.
"Again we have diluted ourselves into believing the myth that Capitalism grew and prospered out of the protestant ethic of hard work and sacrifice. The fact is that Capitalism was build on the exploitation and suffering of black slaves and continues to thrive on the exploitation of the poor – both black and white, both here and abroad. If Negroes and poor whites do not participate in the free flow of wealth within our economy, they will forever be poor, giving their energies, their talents and their limited funds to the consumer market but reaping few benefits and services in return." - Martin Luther King