I heard Kim Geun-sik is being released next year..

In principle, there should be no issue with his release, so why is there such strong opposition to Kim Geun-sik's release?
As far as I know, he is serving his full sentence and being released according to the principle of paying for his crimes; what is the reason for the opposition?
In principle, there is nothing wrong with being released after completing a full sentence. (I heard the sentence was 20 years, though.)