Why is money worth anything? Answer: Because everyone has agreed that it is. You could view that as a banality. Or you could think about that question for years, and still have it blow your mind every time.
I must admit that given the impending and possibly world-wide devastation of our fiat monetary system, this question is actually much more than just an interesting philosophical exercise.
If the US Dollar crashes, and we subsequently witness the crash of Britain's economy, and the dominoes continue to fall with China calling in our then-unpayable loans, umm, exactly what happens next?
On that note, maybe it's time to buy a shotgun...