Its not Stockholm, that does not even exist. It's called empathy and understanding another side of the story. Humans are not black and white, you can't put them into good and evil, unless they have done the crime to satisfy ego's and do not have any remorse for their crimes.
Yeonjo's perspective is biased. His father and family may be good people to him, but to the country, they are not. Yeonjo is discovering that the murderer of his father did not do what he did for some stupid reason. Heeryang had to survive and followed orders. If there is anyone to hate it would be the one who ordered it. But even then, was his father really faultless? Was his father really not a threat to the kingdom? Yeonjo is simply broadening perspectives.
Why are there so many people cheering for MC falling in love with his family’s murderer? Am I the only one here utterly disappointed with the direction the author chose? Why can they never stick with revenge stories and always back to Stockholm syndrome? Does plot not sell well in BL anymore?