This is a very vague question so it is hard to know what sort of discussion you want. Let me just say what I think the main idea of this list (I hope it is the same list you have) is.
To me, the main point of this list of 10 myths is to say that school shootings are not these random, unexplainable things that are not "our" fault. Instead, the authors seem to be saying, school shootings are "our" fault.
I would argue that myths 1-4 and 9 all emphasize this idea. They are telling us that we can and should know who the school shooters are. They give us all sorts of ways of to know who they are and that they are angry. So if we choose not to see these signs, it is our own fault.