Destiny is supposed to be "Hopeful and Inviting". Just because humanity is almost lost, doesn't mean we'll turn into mouthy pirates. In fact, one might argue that after such an event, the survivors would be joined in a common bond of support and brotherhood. This could easily lower hostility, as each of us rely more heavily on each other. But if you still find it unrealistic, remember, it's mythic-sci fi, it doesn't have to be realistic.