Assad tells the Christian minority that the rebels will enforce Shariah law and that they are only safe under his rule. Works the same way with different sects. He says the same thing Mubarak said; that the country would fall apart without him. Unlike Mubarak, he's sowing seeds of division to prevent a unified movement against his dictatorship from forming. A self-fulfilling prophecy.
Syria is probably too much of a basket-case for useful outside involvement.