I do agree with (some of) the general dissatisfaction with the series. I believe that ultimately when it started going down hill was when they felt the need to make his "home world" the hub world with a school for the literal hundreds (at minimum) of sociopathic students who were sent to other worlds to kill demon lords.
I don't have a problem with the premise of the school or the idea that the majority of the others are sociopathic. These things make sense for the reasons others have pointed out. What I do have a problem with is that the organization is large enough for it to be well known (or, bare minimum, known) to the MC, and yet he was so blindsided by it that he literally brought the one he wants to protect and "show the world to" to what is inarguably the most dangerous place for her.
Basically, unless they had absolutely no way to go literally anywhere else, he made the mistake of returning to the most dangerous place where he would have to work extremely hard at not standing out... I.e. he did this to himself.
I don't buy it.
Certainly, if you give an adolescent superpowers and a world that will worship them for killing something objectively human, it's far more likely to result in "damaged goods". Just think about the behavior of most video game players, and apply that to the real world with real people...
And, no, I don't object to his actions this chapter. He has already proven that he will reveal (as much of) himself (as necessary) when something breaks his morals. He... has difficulty containing his emotions under certain circumstances. Honestly it's more surprising that he still has it "together" as much as he does given living and fighting for 30,000 years with only one other person who was only ever semi-sane, until he destroyed her demon lord seed/core...
And, I've lost focus. To not ramble more I leave it here.