This was actually actively propagated by the former Soviet Union. They were at work demoralizing America in the 70s, teaching children in schools about all the bad things America did: emphasizing slavery, the displacement of Native Americans, painting Vietnam as a war of aggression... the goal was to make Americans ashamed of America. It worked beautifully. Hollywood has played its role as well, churning out movie after movie reminding us of slavery and discrimination, depicting anyone conservative as a wife-beating, racist, gay-bashing monster, over and over and over. It's taken about 50 years of relentless brainwashing, which was internalized so thoroughly it continued even after the USSR was no more. But now, here we are.