I believe that South Korea's hands are tied for the moment.
While North Korea and South Korea are still technically at war with each other there is currently the Korean Armistice Agreement (a very fragile cease-fire agreement) in effect, has been since July 1953. In addition to North and South Korea the United Nations in general and the USA in particular would be drug into that rhubarb, instantly. The "hot" war would be on again with the now very real possibility of it getting REALLY hot with a nuclear weapons exchange. Not a desirable situation.
This post was edited by Salt and Red Pepper at October 10, 2017 5:48 AM MDT
S. Korea also imprisons religious individuals. Right now sitting in s. Korean prison cells are young Jehovah's witnesses that were sentenced due to refusing to serve in the military.