When “American Idol” sneezes, American culture catches pneumonia. Every inch of each week’s show is subjected to scrutiny worthy of an International Atomic Energy Agency inspection team. Every misstep comes under a remorseless spotlight. And of all the iffy decisions each contestant makes, none — not picking a terrible song, forgetting a lyric or flubbing an interview segment — is as likely to earn a singer the wrath of the nation as a bad fashion choice. “Pitchy” singing can be forgiven. Skeletons from one’s past are gladly shoved back in the closet. But if you are a 17-year-old singer with a reputation more wholesome than Betty Crocker’s, as David Archuleta’s is, and you step on stage in leather pants, neither God nor man nor the Fox network can save you.