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
