To play the other half of this argument: America engaged in slavery, but also fought its bloodiest war to end it, played a major role in ending the Holocaust and freeing Europe from the Nazis, ended Japan's conquest of Asia, freed South Korea, and brought about through hyperpower probably the longest peace between major powers in millennia, among other notable counterpoints.
It's almost as if the world isn't black and white.
America and everyone else will continue doing both wonderful and terrible things, but we'll keep discussing only the half of those things we disapprove of, especially if it feels like it's helping us win an argument.
Hand-wringing over the past doesn't make tomorrow better, it's a distraction from doing things that will.
To be clear, basically the whole of human history is misery and privation, and only in this era of long peace under the aegis of American hyperpower have we witnessed a glimpse of lasting peace and prosperity.
So, no one will disagree that great wrongs have been wrought, but it seems intellectually dishonest to overlook the staggering good.