That’s actually ahistorical. There were numerous pro-democracy protests, and subsequent massacres by the ROK. Gwang-ju is perhaps the most famous example of the ROK slaughtering countless civilians protesting for democracy, but it happened during wartime as well. Korea’s modern history, North and South, is intensely complicated and messy, and to pretend it’s a simple matter of the US protecting the defenseless South Koreans from the big bad North Koreans is just as wrong as saying that North Korea is 100% good and just.
There’s also the No Gun Ri Massacre, by which American soldiers murdered hundreds of South Korean men, women, and children.
South Korea in particular has a history of military dictatorship, coups, and massacres of pro-democracy civilians, and even in recent years is still having trouble with fascism.