Whence Cometh Moral Outrage?

Everyone seems to have their own definition of morality. Why is that? If morality is "the proper behavior for a person in society", which I think it is, then why is there such disagreement on what constitutes immoral behavior? Or put another way, what causes people to feel "moral outrage" toward certain behaviors and not toward others, and why do some feel it toward a given behavior while another does not? Why the seemingly subjective nature of moral outrage, but not of morality? Got your shovel? Good. Let's dig!
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