Im sorry but you're misapplying the eras. Economic growth in the 1900s wasnt the exploitation of slavery, it was the result of laissez faire and industrialisation. Capitalism at the time exploited the working class. Cheap labor because of continued migration allowed the conglomerates to grow and vertically and horizontally integrate, hence why a direct response to this became Keynesian economics and social democracy became a thing.

Was racism and civil rights an issue of the era? Yes, but national homogeneity was something that was pretty popular at the time as seen by the immigration laws that were passed against Asia. The most similar precedent and probably the steongest case for reparations, which isnt an economic one but of civil justice, is to point to japanese internment. However, the biggest difference was they were compensated immediately, and unfairly, and that they were seen as citizens at the time. Reparations in this case, is just not feasible. Yes there was systemic racism but that still exists. Are asians to be able to sue for reparations in the future if affirmative action is seen as racist? If your answer is no, why? Fundamentally its the same argument, opportunities were taken away. If yes, then how do we calculate the payment?

You seem to be making the assumption that the wealth and production created during the 1900s is a direct result of the profits that plantation owners had but thats not inherently true.