// now entire cultures, even those wholly unconnected with this atrocity, are being implicated//
Not an unreasonable extension of the OP, is it, Jim? Cultures affect behaviour, someone told me recently.
If your culture teaches you that FGM is an honourable practice, or that rape (even of children) is under certain conditions religiously, and therefore morally permissible, then you're not going to change your mind[i simply because you've moved from Lahore or Mogadishu to Manchester or Luton. Are you?
The point and question (implicit in the OP) is to what extent these contributors to diversity are likely to change their [i]behaviour]. Assuming, of course, that in today's multicultural Britain you think they should.