I feel like the Nuremburg trials reached a slightly different conclusion. America's foundational document - its very reason for existence and justification for treason against the crown - declares that all men are created equal and endowed by their Creator with inalienable rights to life, liberty and pursuit of happiness (later formalized in the UN Universal Declaration of Human Rights) and, crucially, citing consent of the governed as the basis for all laws' legitimacy. Laws radically contrary to those fundamental rights, made by a handful of despots, have and had zero legitimacy. It's surprising that you'd claim otherwise.
Nor is that some kind of novel concept of a gradually-evolving society. Looking at what some (particularly in early American history) would say is an even higher authority, a spokesperson for that Creator himself, it's said to do to others as you'd have them do to you, for this fulfills the law and prophets. Condemnation of and expecting restitution for the brutality of American chattel slavery is not imposing recent values or laws on a less developed society, it's holding them to their own foundational legislative principles and even more ancient and universal moral ones.
You understand that this is an idiosyncratic if not almost unique notion of racism, of course? Many proponents of Jim Crow laws under the slogan of 'separate but equal' would have insisted that their system was not racist. You do agree that it was a racist system, I assume? Obviously the same must be true of one which is not equal, one which (with advocates' full knowledge regardless of professed intent) disproportionately harms a historically poorer segment of society never compensated for the brutalities and disadvantages inflicted on them.
It's a big topic, and <5000 characters is hardly an onerous read.