Milgram is an experience that want you to answer or at least think on difficult question on how to judge people for murder. The murders it present can be generally divided in 2 categories:
1- no conventional murder took place but someone died because of the actions of someone else (ex: pushed to suicide), in that case how do we cut a line in the domino effect on guilty or not guilty?
2- actual murder happened, and in that case the context and the reason for murder is what's interesting to discuss. Everyone who has to make judgement on a murder will try to learn more on the why and how of the case in order to make a decision.
The case that I find the most interesting is Amane's, because yes, I think children should be judged differently than adults and because I never had to think about the possibility of a child committing murder before. But to just ask the question "a child killed someone, what do we do now?" is not really thought provoking, let alone story telling. Adults don't kill for no reason, and for a child to kill mean that something very wrong must have taken place.
If Milgram just said "idk the child is evil and they killed, what now?", I would thing it is uninterested in it's own premise and can't bother to actually write anything. Thankfully it did bother telling an actual story.
Anyway, Mikoto has an evil alter that killed evilly, what now?