CAIRO, Egypt — Expressions of shame and self-reproach swept the Arab world yesterday as Muslims mourned the deaths of Russian schoolchildren and voiced unusually critical condemnations of the social ills widely blamed here for breeding terrorism. The Arab world has watched with mounting disgust in recent weeks as a wave of civilian hostages — some of them Arabs and Muslims — were slaughtered by masked insurgents in Iraq. This weekend, newspapers and satellite channels were dominated by pictures of bloodied, naked children in southern Russia fleeing armed guerrillas suspected to be Islamic rebels supporting an independent Chechyna. Many Arabs faced...