Never try to solve a problem regarding the players by any “in-game” means like punishing or killing off their characters.
If the players are more interested in killing, then killing some more, a campaign like the Dark Symmetry Campaign is not for them. They might like a more military campaign, like an assault on a Citadel or so, much better than an investigative campaign.
TALK to your players.
Tell them, what YOU like in a Mutant Chronicles game. Ask them, what they like. - And if your interests don’t mesh to any degree, then play something else.
When I put the effort and work into running a campaign as a GM, I do want MY share of fun out of the game. I usually enjoy playing NPCs, presenting puzzles, and from time to time some tactical combat situation. If my players wanted something else, like murder everything that moves, then that won’t work and I look for other players or run something else entirely.
As a player in the Dark Symmetry Campaign this was one of the most epic campaigns I have ever played in. We had intense moments, character development, cunning plans and bad luck making bad situations even worse, but we pulled through. That was possible, because all the players tried to play law men, cops from Luna PD with a cop mindset. Meaning, even while on Fuji-Station you don’t go about murdering innocents left and right. You play a responsible human being, NOT a murderous heretic ■■■■■■■. - And that is, what makes for me Mutant Chronicles so intriguing. Mere weak human beings trying to stand up agains the evil of the Dark Soul - and different to Call of Cthulhu, they actually might win - or at least thwart the Dark Soul’s plans for a few centuries.
As I said: Solve out-game problems regarding your players only out-game. In-game “solutions” don’t exist.