@Solipsist About the "demon" rank and "enlightened" rank, it has nothing to do with being "good" or "bad". Besides, good or bad is all in the eye of the beholder anyway, the world isn't so black and white. If someone gets in your way or does sth. that's disadvantageous to you, they're "bad" to you. But at the same time, they might be doing that to help someone else, which would mean they're "good" to that person (and you'd probably be "bad" to them).
Either way, as far as my limited experience with Korean ( and Chinese) martial arts stories goes, the Murim world is divided in some sort of "Dark" faction and a "White" faction. The highest ranks/strongest within the sections are either called "Demons" (dark faction) or "Sovereigns/Kings/Emperors"(white faction). The names change slightly depending on the translators/story. Also, I'm not sure what they base the division on, I'm guessing it has to do with the type of martial arts you use. Both factions are usually also at odds with each other, either full on at war, or more underhanded and verbally during relative peace time.
However, I understand it's easy to get confused by it (the first times I read about it I was as well), since the white faction can also be called the "Righteous" or "Heavenly" faction, while the dark one can get names with a more negative connotation. Even so, in the stories I've read, they've never absolutely equalized them with straight-out being good or evil, but it came mostly down as a name. Of course you'll get members of the white sect saying those of the dark one they're evil and stuff, but that's again a matter of my first paragraph. The factions aren't friends with each other, after all. The division is just yet another way of "Us and Them, if you're not with us you're with them, ergo the enemy". In other words, another way of causing strife.
If someone has a more comprehensive (and probably more correct) explanation, feel free to do so. If I offended someone with my explanation because the Murim stuff might be part of Asian history of which I don't know Jack about (aside from the biggest events), and with my European upbringing I probably look like an ignorant asshat, I'm sorry.
