When word started to arrive earlier this month that Justin Bieber had put on a pretty weird performance for the first of his two Coachella sets, my protective instinct kicked in. Discovered on YouTube when he was young and that platform was even younger, Bieber is pop culture’s great test case for what growing up online and in public does to a person. Ever-seesawing between scandals and successes, he’s conveyed a lesson that the world keeps relearning: We need to give our social-media stars a