Not confronting our problems
In my opinion, I believe this may be what the film is actually about. How we, as a society, aren't caring about the things that should truly matter to us, how we don't heed the warnings that are presented to us, and how we run for comfort in the face of problems rather than facing and dealing with them head-on.
Like Julia Roberts's character and her impromptu shooting off for a vacation when things aren't feeling right, or the daughter's constant search for Friends episodes when the world is obviously crumbling around her, I see the message being about how we keep ignoring signs of danger (and, subsequently, taking action to do something about it) in favor of fun, comfort, media, denial, and escapism.
Like the West Wing episode the girl quotes, "God" keeps showing us that danger is looming and that we should be concerned and proactive in saving ourselves, but we continuously ignore all of the warnings, thinking that it will all work out on its own and that someone else will take care of the problem (and take care of us). We, meanwhile, not wanting to think about it, just keep ourselves distracted, physically and mentally running away from our problems (i.e., leaving the world behind). We see the ship heading straight for us, so to speak, and sit there doing nothing until it's almost too late.
I think that's what was going on with that abrupt last scene that so many appear to dislike. I don't think this movie, though, was about what the attack specifically was, who caused it, or any of the details about what's going on as a result of it. Nor is it about how any of that resolves. I think it was merely about the fact that an attack did happen and that there were signs that we ignored (the actual enemy, I believe, was intentionally left ambiguous to emphasize how many threats from potential enemies that we don't think about every day).
As GH was speaking about, in reference to his clients, we keep making the same mistakes over and over, even after those types of mistakes have already caused us to lose everything. This, I believe, is what was going on during that final scene at the bunker. Harkening back to that West Wing quote again, that life-saving bunker and its warnings of radiation levels was yet another example of God throwing the characters a warning and a life raft. And how do we react? We flip on Friends. We ignore it, choose not to think about it, and opt for distracting escapism that will make us feel better but ultimately result in our demise.