Let me repeat: facing Aragami outside the fortress walls, there was a terrorist attack inside the wall. For instance ( according to side materials), just a month after the Aegis event (between the first game's ending and Burst), there was a terrorist attack inside the Far East Branch.
The problem is, to use the God Arcs they need to inject Oracle Cells into their body, with only their bracelet to contain them from running wild with your body.
And they eat up everything they come in contact with, including radiation, so not only humans are in danger, so is every other living thing on Earth.though ironically, since some of the Aragamis manage to adapt photosynthesis to compensate the loss of plants, the world is not doomed immediately. As of Rage Burst, it's still not clear what, or when, created the these cells (and subsequently Aragamis), be it human's creation, or the Earth's answer to human beings' acts.
Imagine how bad the world has become when circuses (beastmasters), seasonal flowers and even dogs become rare sights, as Resurrection revealed.