The Holocaust
How about you own up and accept you killed 10 million people and would gladly have do it again if you had the chance (and you won't, thank god).
Racism
Because your skin colour and ancestry mean everything, of course.
Jim Crow laws
Because being black means you should have as few rights whatsoever and must be perpetually subservient.
The Ku Klux Klan
Because using mob violence and terrorism to enforce the above is perfectly good and just.
Hitler
Screwing over your own country and your own people more than any ruler up until that point had ever done in your horrifically naive decision making process and flawed views of your own competence is exactly what all rulers should strive for.
Slavery
Because a certain class of people should have zero rights whatsoever and should be forced to work for free and be subject to abuse if they complain or don't do their job well enough. That's great, isn't it, perfect economics, logical morality.
Segregation
Because having separate drinking fountains for people whose only difference is their fucking skin colour makes total sense. "Separate but equal" is completely illogical, even if somehow it actually could literally be "separate but equal."
They are afraid that one day, we won't feel sorry for them when we stop them from exploiting us.
If you like Hitler so much, why not just own up to the Holocaust since you seem so eager to do another one. Wouldn't that make him horribly incompetent if he had the chance to kill millions of Jews and didn't kill any/barely killed any of them?