I can’t say that I have any special insight into how Broadway manages to sustain itself, but the fact that a Green Day musical exists and is profitable is so bewilderingly strange that it chills me to the bone. The touring company for American Idiot, a rock opera based on the 2004 album of the same name, descends upon Nashville for a three-night stand of flailing wildly against the suburbs, television and the military. Also, American Idol rejects and nameless manic pixie dream girls performing aerial dance. You know, punk stuff. Despite what it lacks in depth, American Idiot manages to convey a loose, kinetic spirit that won it a round of Tony nominations for a reason — not because it’s a particularly smart musical (it isn’t), but because it gives people the sort of safe, Hot Topic version of punk rock that they’re looking for.