In the mid-1980s, \u201cDo They Know It\u2019s Christmas?\u201d and \u201cWe Are the World\u201d gathered dozens of the biggest stars in music to put on a show for a good cause. The two songs spawned imitators, but today, the charity megasingle is a relic of pop music\u2019s past, except around the holidays. This month, we examine how good intentions, pique, excess, and vanity led to the rise and fall of the do-gooder celebrity pop song.\xa0 \nEmail: hitparade@slate.com \xa0\nLearn more about your ad choices. Visit megaphone.fm/adchoices