In the play, Pierre (the Shadow) kidnaps Margot to give her "romance". The Riffs object to this, understandably, because it puts them in danger from the French. But he doesn't, so eventually he's set up to fight his own father, and when he refuses, they exile him for being a coward. It's kind of a bad message. Basically, "It's perfectly OK to throw away your ideals and your friends for your true love."