I see it as a religious allegory to radical extremist that would go the far lengths to kill themselves in the name of their God, I think there's moments when people in the movie looks outside and says something on the lines of "it's so beautiful..." also they hear the voices of dead close ones as well, almost as if they are bordering the spiritual and psychical world. If they are exposed to this then maybe its because they are peering a bit into heaven or their idea of a heaven and its so beautiful that because dying is the only way to go there they would do whatever it takes to kill themselves and go there.