My own sense is that we have to work towards a functioning pluralistic society, if only so that we can all live decent and peaceful lives. Acknowledging the difficulty of this aim in no way diminishes its validity and rightness. Of course it will be difficult getting people of different religions, cultures, nations, and ethnicities to live together peaceably - to hold otherwise would require a dismissal or ignorance of most of human history.
Unwillingness to admit this difficulty is also motivated - particularly among those on the left - by a fear of guilt by resemblance. Expressing anything circumspect about multiculturalism could see you misidentified as one of those right-wing enemies who express similar sentiments - it might even somehow put you on a slippery slope towards holding the same opinions. Best, then, to avoid circumspection.
But this is nonsense. The most worthwhile prizes, a pluralistic society being one of them, are often difficult to achieve, and achieving them involves being circumspect and facing the hard questions.
So here's what I think are some hard questions. Muslim clerics have been vocal in their denunciation of the killings - as e.g. here. Is it, however, the right sort of denunciation, and is it right for us to ask the clerics for more? They agree that the killing of the journalists was wrong, but the wrongness of murder is a fairly easily achieved piece of common ground, and falls short of a trickier and more important confrontation (and hopefully, ultimately, reconciliation) between the religious and the secular:
we can all agree the murders violated the sanctity of human life, but do the clerics agree that freedom of speech enjoys a similar sanctity and that its violation is a large part of the wrong committed by the murderers?
Do the clerics agree that the murderers' right to act on their indignation, however justified, was always curtailed by the need to protect the free speech of others (indeed, of all) and not just the lives of others?
Do they accept the reason for this curtailment, which is that protecting freedom of speech is a greater and/or more necessary virtue than religious observance?
These are not leading questions - 'if they say "no" to any of them then let's deport them' - and I do not think they are a means of identifying deviancy or 'enemy' thinking - the last one would probably prove tricky across our entire society, not just for followers of Islam. But it's hugely important right now that we see eye-to-eye with the Muslim community, and work out where we all stand, and what sort of understanding we can come to. So let's have at it.