Any drama where the protagonist is faced with a situation where he/she can kill their enemy knowing if they don't pull the trigger the consequences are worse than if they did and does pull the trigger. 

Basically I'm looking for a drama where all the "good"paths leads to death and only be recognizing this will the protagonists survive and perhaps change the world where" good" ppl can survive facing similar way points. 

And it doesn't count if the protagonist is already a bad guy. I want the moral dilemma and the maturing and the shock of a good protagonist doing something "evil" to do something good for the big picture or to save a loved one.. 

Cruel City - little and big shocks are in every episode, not only ML ,  many characters are walking on line of moral (wont say more because of spoilers) but this is really good and mature drama

Arthdal Chronicles - would say same, but there aren't triggers ))) it's AU old time, very very good drama, very layered characters, everyone are bad and good same times, there are moral crisis and decisions too (at list for one character (he wasn't angel, but had some moral line, but situations made him become tyrant), but you will see many situations that maybe isn't 100% what you described but similar feelings)

The Smile Has Left Your Eyes 

Kill It ML is anti hero and killer from the beginning but there are few good "pull the trigger" situations, it's good drama and quite short

The Innocent Man really good guy becomes the one who can pull the trigger, not to save world but people and world make him different man

Warrior Baek Dong Soo SML becomes dark/killer, there are few times when I didn't thought he would do it but... also he is very very charismatic, great character, dark sexy )))

p.s.

When the Devil Calls Your Name there isn't trigger and he's not doing something bad for greater good, but I saw interesting moral questions there, what can common not "bad" man do for selfish interests, is evil some god-like devil or we already have that evil inside us. Usually that questions and naked morality of human isn't in dramas so I think it was interesting drama and thought mention it too

Hmmnnn not really what you ate looking for since choosing the dark side didnt carry a motale dilemma at of the drama. They are past that stage, and ate pn the stage of planning and execution:

  • Mr.Hiragii's Homeroom - a teacher who kidnaps his students for a lesson. Though there is no moral dilemna cause he really planned it all
  • Nirvana in Fire - saster strategist who will navigate through the dirty political pool of royal issues
  • Song of Glory
  • Non Protagonist Character:
    • Stranger  - Chief Prosecutor Lee Chanhjoon
    • Designated Survivor - secretary of staff Han JooSeung
  • Kill it
  • Maou
  • Orthros no inu
  • Extracurricular