(Author's Note: The main character is not standing on the side of monsters, nor is he against humanity; he is not that complex. At the time, the main character was not thinking of anything too complicated. He was just standing on Dumby's side.
If I had written it such that the main character stops Dumby and keeps him from killing the humans, would everyone have liked that instead? I fear, even more people would have ended up scolding me.
Main characters that decisively kill all their foes are liked by many. I like them too, because they are enjoyable to write about; little brainpower required, simple and violent. But with how the story has developed, I think it's unreasonable for Gao Peng to turn into such a character. It's just too sudden. Personality change is a process, and it requires time.
As a person ages, their personality and views on the world will change.