The Khmer Rouge murdered 25% of the country! 2 million people!! https://sfi.usc.edu/collections/cambodian-genocide
The Viet Cong were also horrible (excepting, of course, their intervention in Cambodia against the Khmer Rouge!) and devastated Vietnam, and the CPV rules it with an iron fist to this day.
Communism really is and was extremely, horribly bad.
In South Korea, the seemingly insane plan of the US (install a pro-Western dictator as a bulwark against Communism, and eventually transition to a liberal democracy) eventually worked. The Korean War pre-dates Kissinger's rise to power, but his overall principle of oppose-Communism-no-matter-what seems kind of reasonable, even in hindsight.
Anti-communist dictatorships and militias were often terrible, too, but it is really hard to be worse than Communists.