There's a heavy dose of shame and denialism too. To be told your whole life that you are the good guys and that your country gets into every war for noble reasons, you have to really reconcile atrocities in a way that doesn't conflict with that myth. To do so otherwise is admit your entire upbringing is a lie, your leaders are malicious psychopaths, and that you've been complicit in voting for them your whole life. That can really really break people. It's a greatly traumatic thing and is on par with losing your religion or estranging yourself from family.

I'd say for the majority of American liberals, they understandably have a difficult time facing the truth. Because the truth is fucking dark.

Every aspect of culture and education in the US is dedicated to drilling into the minds of people that the US are the most good, the most just, the most honest, that their systems of governance are based on these values, and the majority of people work hard towards maintaining that.

So when a USonian is faced with this narrative being broken, they fall back into cognitive dissonance. It's only recently we've seen a reversal of this to a significant scale, but ask anyone and they'll likely tell you that they still believe these things were true a couple decades ago and it's only now that the US has become bad.

Whatever the US has accused communists of doing to their people, the US has already perfected it.