I have lived and worked in Muslim areas of Paris, Gazouille, and the people I knew there were ordinary, hardworking, working-class people. Most were only nominally Muslim and kept certain traditions for tradition's sake, but didn't really practise the religion.
I know several people who were born into muslim families, but who have left the religion, including one man who changed his name by deed poll to something with no religious connotations because he no longer wanted to be associated with that culture!
Those who choose to stay, IMO, are condoning the recent turn towards fanaticism the religion has taken. If they really disagree with terrorism sexism etc, they should be working hard to reform their religion to adopt more modern positions (like the Reform/Liberal Jewish movements have done - removing the sexist rules and traditions and modernising the religion), or leaving it in droves!
Staying and doing nothing is tantamount to agreeing.