Whether procuring firearms at a bank or offering terrifying security-camera footage from the Littleton, Colo., high school massacre, liberal tinderbox Michael Moore achieves an unprecedented balance of horror and humor in his dissection of violence in America. The subject matter is sobering indeed, yet you can't help but chuckle at his irreverent ''South Park''-esque cartoon encapsulating the country's brutal past, or when the creepy brother of an Oklahoma City bombing convict announces, sans irony, ''There's wackos out there.'' Much like the mockumentaries of Christopher Guest, Bowling For Columbine provokes laughs when peeling back the layers of absurdity that underpin our society. The frightening difference, of course, is that Moore's movie is all too real. EXTRAS Never one to skimp on a little self-promotion, the director includes footage from several of his live appearances and a frank 15-minute defense of his controversial Best Documentary Feature Oscar acceptance speech: ''At the end of the day, I'm Michael Moore -- what else was I going to do?''