I think OP's point - and a fair one - is that most, if not all countries have skeletons in their closet. Who is to say that the Holocaust dwarfs all other horrors just because it is the most famous. The United States' genocide of Native Americans was pretty atrocious, and lots of its recent and current military involvement - secret torture, lies, and so on. So why shouldn't Americans be made to feel uncomfortable about their country's history at times?

(Granted, I think there are plenty of occasions where Americans are the bad guys, but yeah.)