I'm gonna have to agree with Sera. The MC is being too inconsistent in his reasoning. One chapter he is refusing to kill animals or demons that are inherently dangerous to humans, the next he's deciding to use rats to experiment on, and another chapter where he wants to outright heal dangerous demons and let them go, and the next refusing to kill again, before now when he's decided to poison fire rats. The fuck is this guy's deal. What is his moral code? He's way too flip-floppy, it's getting annoying. He's acting so fucking high and mighty all the time, "we can't do that, it's not right --- except when it is right, which is when I decide it is, entirely arbitrarily".
The fact he doesn't explain his plans or reasoning until during or after his plans are put into action, or when another character practically has to scream and beat it out of him is ridiculously annoying and frustrating. I think the author thinks this kind of aloofness is cute or cool or whatever, but it's just stupid. I want to smack the MC across the fucking ears until he just stops. Stops what? Just stops.