"I'm thinking it is insecurity and youth in almost every case."
Could also be a form of tribalism caused by a inner need to belong somewhere. Although that's closely related to insecurity.
Or a pseudo-religious zeal, in other words an application of religious feelings towards some mundane object/person/group/whatever. This one is pretty dangerous, because it invariably takes criticism as an attack towards the holiness of...whatever it was that you supposedly treaded on. There can be only one kind of response to that wretched infidel. Only the righteous wrath shall do. And no holds shall be barred in the holy war.