CAIRO—Mobs of ordinary Egyptians joined with soldiers to drive pro-democracy protesters from their encampment in Tahrir Square here Monday, showing how far the uprising's early heroes have fallen in the eyes of the public.

Six months after young, liberal activists helped lead the popular movement that ousted President Hosni Mubarak, the hard core of these protesters was forcibly dispersed by the troops. Some Egyptians lined the street to applaud the army. Others ganged up on the activists as they retreated from the square...