Why France is banning Muslim clothing in schools (again)

EVERY FEW years the French get worked up about an item of religious clothing that they deem inappropriate in the classroom. This time a controversy has broken out at la rentrée, the start of the new school year, over a government decision to ban from state schools the abaya, a full-length robe worn by some Muslim girls for modesty. To people in countries with a tradition of liberal multiculturalism, the ban looks like an unacceptable infringement of the right to religious expression. To defenders of a strict version of French secularism, it is a measure necessary to protect the republic from religious interference. Why is France so worried about Muslim dress in its schools?