For those telling him to kill the guy, remember that the MC is human, he wouldn't want to directly get blood on his hands, and even cold people aren't completely emotionless, there will be feelings of regret and disgust and killing a person is different to killing monsters, while they are both lives ones for a job and the other doesn't have any benefit other than getting rid of a future problem, and will the guy really be confident enough after he was beaten naked, humans aren't made to easily kill each other unless there are mental problems, so with the MC being a human like us and not one from that world, they kept the MC human instead of just making him kill that easily, the man easily took his opponent out SEO the threat wasn't enough to kick the fight or flight instinct, and what psyco would one have to be to have the first thought after defeating someone to kill them, the MC isn't completely apathetic and his previous life wasn't something that would make him have the first thought of killing someone, he needs more time in this new world to completely accept that he has the ability to kill someone and he needs to grow to be able to be use to it, so there will be a period where he won't kill even after his first kill since it's not easy to kill someone and get use to it unless you are a crazy person, basically why would the MC kill someone if he has morals, and if you say he doesn't since he didn't save people, that's human nature to not interfere and put yourself in danger, it's not moraly right but it makes sense, the MC having morals means he won't easily kill/cause harm, the most we can expect currently is threats, at least that's what I think but who knows what the author did