Two words: Fuck Yeah!
I loved this movie and laughed so hard during the sex scenes and puke scenes that I almost passed out. Loved the songs: "America: Fuck Yeah", "Pearl Harbor sucked and I love you", "Everyone has AIDS!", "You need a montage!" "I'm so Ronry"
The movie satirizes both American cowboy mentality and left-wing actors as political experts, but apparently some critics don't like it because of it's "nihilism" (refusing to pick sides and have an "agenda") And of course, because it attacks the hollywood liberals, they assume the movie is Pro Bush, even though it makes fun of Intelligence, US overly aggressive military campaigns, patriotism, etc
Pretty much the only "moral lesson" of the film is the final Dicks, Pussies, and Assholes speech which seeks to partially explain and forgive America's behavior.