> "Killing" has rarely singled out one specific ground of people and subjugated them for centuries

While the term holocaust mainly refers to what the Jews went through during WWII, slavery encompassed not just blacks, but many other races including whites. The problem here is that the "discussion" happening is extremely US centric, that non-Americans are either looking at it as absurd, or they've become so Americanized that they think it's correct, meaning they also have no proper critical thinking skills and are easily swayed.