The scene in question is when aoyama is about to blast izuku with his naval laser; We see the effect for danger sense activate. And like he said in his battle against class 1a; It only reacts when theres malicious intent. Izuku told his classmates that his presence was a danger to them as all for one could kill them, so he had to leave.
The issue is that horikoshi barely gave any proper screen time and characterization to most of the students, which makes the idea of class 1a being a family fall flat. Then theres the issue that there is just too many of them, which resulted in lots of them doing nothing for most of the story. Not only that but momo has a very methodical nature and is one of the smartest in class 1a. If bakugou, todoroki or deku went evil, someone would probably come along and catch them before they mastered their powers. At this point in the story, what the reader should be feeling is a real sense of danger for our characters, but instead they feel invincible because none of them get killed or even seriously injured. To contrast, jjk has me feeling worried for the characters because you don't know what's going to happen to them.
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