Why does the MC join a group which is discreetly hostile towards him? Bad decision, MC.
Based on my understanding, His original plan was to use them and kill them for a mission that is open to everyone who has Ki because he knew that she was the one who killed her own teammates for the same reward. He wouldn't have to feel bad for killing them instead of innocent people because he needed to get stronger. The mission is to kill 7 or 8 players I think and things changes after our mc realizes that the dungeon they went in also supports the mission. Plus, if he wanted to climb up to the top, he needs to face stronger enemies.
(I rephrase my words so it's easier to understand) .. I've looked back at the chapters again and the mission was called the "hell condition" reward, you basically have to sacrifice 9 players to exchange for rewards and skills. He didn't want to be the type of person to kill innocent players so he decided to target wei xi group (I think thats her name) , he already know she's cruel because that's how she was able to level up by killing her own teammates using the hell condition reward. As I said, things took a turn when he realizes the dungeon they went in actually activates the hell condition on its own so another reason he shouldn't feel bad for killing any of them.
If he trusts his words, that means MC is a moron.
MC is already not smart when he didn't shoot at that leader's head.