DAMASCUS, Syria — In a terrace cafe within earshot of army artillery, a 28-year-old graduate student wept as she confessed that she had stopped planning antigovernment protests and delivering medical supplies to rebel-held towns. Khaled, 33, a former protester who fled Damascus after being tortured and fired from his bank post, quit his job in Turkey with the exile opposition, disillusioned and saying that he wished the uprising “had never happened.” In the Syrian city of Homs, a rebel fighter, Abu Firas, 30, recently put down the gun his wife had sold her jewelry to buy, disgusted with his commanders,...