In normal times, people are always disagreeing with one another about anything and everything. This politician said something that one person finds deeply offensive, while her neighbour agrees with the pronouncement. This is the normal way of things. You get a lot of different opinions and people are firing off their views about a broad range of things all at the same time. But when things get so focused that only one thing is discussed you start to feel the force of unanimity. Unanimity is what the terrorists want to inspire in the west when they attack people in the cafes and restaurants as they did two nights ago in Paris. What they want to do is to foment so much unhappiness with the muslim population living in the secular west that they force those muslims living there to go to the Islamic State to live. They want to drive the muslims out of France and unanimity - or purity - is their friend.
Purity of feeling, a unanimity of opinion, about something is the enemy of tolerance and plurality. It is of course easier because when it obtains people generally are inspired to feel like part of something. It's comfortable. And comforting. But is it a good thing to be part of? I think not. Tribalism is when you "other" one group at the expense of another group. By othering muslims we play into the hands of ISIS and start to operate in a way that they sympathise with. What we should be doing is arguing about how to deal with this crisis, in the normal way of fractious westerners everywhere. Arguing is good.
It might seem more difficult and when there are arguments people might feel more alone, but it is the activity that is at the very core of democracy. Diversity of viewpoints is good, unanimity of opinion is bad. Let's agree to disagree. A false feeling of unanimity might seem like a good and virtuous thing but in reality is is paving the way to our destruction.