Well, you know, they were either "not human" (or 3/5 in some cases) or "terrorists" or "reds" (those millions in Laos and Cambodia must have fell in that category, one would hope) or something like that. Not sure how they categorized those 200,000 or so peasants in Guatemala, but hey, out of sight, out mind, eh?

In recent US history as well as ancient history, "them" vs "us" has been enough justification to satisfy the public in any time period. It's not that few in the US cared about bombing "commies" in Laos and Cambodia, it's that being "red" made much less difference than being "them". This is tribalism at its finest (or worst, take your pick).

The genocide of native americans, Stalin, Hitler, Churchill starving million in India because he thought them to be less human, the transatlantic slave trade....all just minor blemishes in an otherwise great culture.

Perhaps the whole idea of "culture/ideology" is flawed and progress happens not within a culture but by specifically rejecting cultural and ideological norms.

That itself is a culture/ideology though. That is sort of the culture of the west in fact, to move forward, and whatever isn't helping move forward gets left behind.