Good take. I've been to Cambodia and seen the Tuol Sleng Genocide Museum in Phnom Penh (converted from a high school to a prison for political prisoners). It's pretty chilling.
But we do need to see these things as a chain of events rather than isolated actions. Indeed, the meddling US ruling class has a lot of responsibility. I'd say that China and the USSR also have some blame, using other nations as pawns, and perhaps precipitating such a brutal regime when it would not have been necessary. They rushed through it and as usually happens when you do that, they fucked up.
Despite best efforts to prevent the red menace from spreading, now nominally "Communist" Vietnam is a rising economic power. Visit sometime … Houses going up everywhere, and many people finally have enough money to leave if that's what they choose to do. I didn't get a sense from the people that the government was anything but something done to them rather than something they were part of, though, so I would guess it's another sham socialism, with maybe some elements to control the worst of capitalism…