Even if people find the existing laws insufficient or not to their tastes, that does not give them the right to come up with and enforce their own private laws which are contradictory and sometimes even break the laws of the state in which they live. A society, at it's most basic level, is a group of people bound by the same laws. If one subgroup within that society decides to have their own laws that breeds fear, hatred and resentment, in both groups (in this case Europeans and Muslims). That will just lead to an increase in religiously motivated attacks, again by both groups, and will ultimately destabilise the existing society, which cannot be let happen.