I'd also like to point out one thing that may help you understand why I think banning these garments will have no effect on the level of violence in France. The dramatic rise in violence, gang rapes and murders committed against women in French suburbs is a relatively recent phenomena. The generation of women being targetted is young. Their mothers never went through this. Women wearing hijabs was a rarity in France up to the late 80s, early 90s. All of a sudden, some 15 to 20 years ago, young Muslim men in the poor suburbs started systematically attacking and/or raping young girls who they considered not "pious" enough. This is the reason many girls started to wear the hijab, to protect themselves from these attacks.
You see, the problem started at a time when French Muslim women were NOT wearing these clothes. They were being raised in a country that taught them they were men's equals in every respect. They behaved and dressed exactly the same as the native French women. Until, seemingly out of the blue, the abuse started. When hardly anyone was wearing Islamic dress anywhere in the country and practially no one was expected to. Clothes are not the problem. No matter what they wear, if the root of the problem is not addressed, these girls will continue to be abused by out of control, unemployed, radicalized young men.