This comparison was widely observed by Black intellectuals who were the direct descendants of slaves in the era of Reconstruction era and beyond, so it’s funny to class it as “rude.”
Capitalism emerged out of feudalism, maintained many of its hierarchical qualities and power dynamics, and replaced a bound peasant labor force with one with varying degrees of freedom. At the bottom of this hierarchy in the U.S. was a racialized slave caste that was later freed from this this specific form of bondage, but kept me in much the same position through other means. Various forms of current and historical struggle have brought us to greater equality, but it’s difficult to argue that wage labor in the U.S. wasn’t shaped and defined by the presence of slavery. How could it not be?