I tend to take the song much more literally - that it actually is about two people who fell in love during a war, and the knowledge that they might die any day now makes them appreciate the world that much more. Also, they want to make the most of the world while they're there - carpe diem, if you will. Put beside the fact that they have to fight for everything they have right now, it seems almost a crime that something that makes them so happy doesn't have to be fought for.
I tend to take the song much more literally - that it actually is about two people who fell in love during a war, and the knowledge that they might die any day now makes them appreciate the world that much more. Also, they want to make the most of the world while they're there - carpe diem, if you will. Put beside the fact that they have to fight for everything they have right now, it seems almost a crime that something that makes them so happy doesn't have to be fought for.