Speaking of it being super dumb regarding murder, don't forget how when Shiki finally does kill the deranged psychopath, the glasses dude's reaction is basically 'lol that's fine' even though he spent the whole movie being adamantly against it. Ugh, it couldn't even be consistent.
This specific aspect didn't bother me actually.
There's a few ways to frame this I think, but my understanding/interpretation is that Kokutou cares more about Shiki than he does about morals. In other words I think his primary objection is not "You shouldn't kill people because killing is bad", but instead "You shouldn't kill people because the process of becoming a murderer will be painful for you, since you recognize that killing is bad." This isn't an after-the-fact rationalization either because I distinctly remember internally calling out Kokutou's declaration of "I'll never forgive you if you kill him" as a bluff when they were having the phone conversation before anything in the finale had occurred. ---
Congratulations to BK_Sheikah00, this year's guru to achieve contest enlightenment!