This song is said to be about Courtney Love. It refers to her dragging Kurt Cobain intro drugs, and ultimately being the cause of his suicide. "Why'd you have to go and let it die" most likely means why'd you have to go and let him die, or let Nirvana die in general.
Dave Grohl has said of the song: "It's a song that's written about feeling helpless to someone else's demise. I've seen people lose it all to drugs and heartbreak and death. It's happened more than once in my life, but the one that's most noted is Kurt. And there are a lot of people that I've been angry with in my life, but the one that's most noted is Courtney. So it's pretty obvious to me that those correlations are going to pop up every now and again."
Ian - Lakeville, MA